Quokka #2 (node: v8.11.3)

Creates a function that accepts up to n arguments, ignoring any additional arguments.

Call the provided function, fn, with up to n arguments, using Array.prototype.slice(0,n) and the spread operator (...).

Code

const ary = (fn, n) => (...args) => fn(...args.slice(0, n));

Example

const firstTwoMax = ary(Math.max, 2);
[[2, 6, 'a'], [8, 4, 6], [10]].map(x => firstTwoMax(...x)); // [6, 8, 10]

Given a key and a set of arguments, call them when given a context. Primarily useful in composition.

Use a closure to call a stored key with stored arguments.

Code

const call = (key, ...args) => context => context[key](...args);

Example

Promise.resolve([1, 2, 3])
 .then(call('map', x => 2 * x))
 .then(console.log); //[ 2, 4, 6 ]
const map = call.bind(null, 'map');
Promise.resolve([1, 2, 3])
 .then(map(x => 2 * x))
 .then(console.log); //[ 2, 4, 6 ]

Changes a function that accepts an array into a variadic function.

Given a function, return a closure that collects all inputs into an array-accepting function.

Code

const collectInto = fn => (...args) => fn(args);

Example

const Pall = collectInto(Promise.all.bind(Promise));
let p1 = Promise.resolve(1);
let p2 = Promise.resolve(2);
let p3 = new Promise(resolve => setTimeout(resolve, 2000, 3));
Pall(p1, p2, p3).then(console.log); // [1, 2, 3] (after about 2 seconds)

Flip takes a function as an argument, then makes the first argument the last.

Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.

Code

const flip = fn => (first, ...rest) => fn(...rest, first);

Example

let a = { name: 'John Smith' };
let b = {};
const mergeFrom = flip(Object.assign);
let mergePerson = mergeFrom.bind(null, a);
mergePerson(b); // == b
b = {};
Object.assign(b, a); // == b

Creates a function that invokes each provided function with the arguments it receives and returns the results.

Use Array.prototype.map() and Function.prototype.apply() to apply each function to the given arguments.

Code

const over = (...fns) => (...args) => fns.map(fn => fn.apply(null, args));

Example

const minMax = over(Math.min, Math.max);
minMax(1, 2, 3, 4, 5); // [1,5]

Creates a function that invokes the provided function with its arguments transformed.

Use Array.prototype.map() to apply transforms to args in combination with the spread operator (...) to pass the transformed arguments to fn.

Code

const overArgs = (fn, transforms) => (...args) => fn(...args.map((val, i) => transforms[i](val)));

Example

const square = n => n * n;
const double = n => n * 2;
const fn = overArgs((x, y) => [x, y], [square, double]);
fn(9, 3); // [81, 6]

Performs left-to-right function composition for asynchronous functions.

Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition using Promise.then(). The functions can return a combination of: simple values, Promise's, or they can be defined as async ones returning through await. All functions must be unary.

Code

const pipeAsyncFunctions = (...fns) => arg => fns.reduce((p, f) => p.then(f), Promise.resolve(arg));

Example

const sum = pipeAsyncFunctions(
 x => x + 1,
 x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)),
 x => x + 3,
 async x => (await x) + 4
);
(async () => {
 console.log(await sum(5)); // 15 (after one second)
})();

Performs left-to-right function composition.

Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.

Code

const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));

Example

const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = pipeFunctions(multiply, add5);
multiplyAndAdd5(5, 2); // 15

Converts an asynchronous function to return a promise.

Use currying to return a function returning a Promise that calls the original function. Use the ...rest operator to pass in all the parameters.

In Node 8+, you can use util.promisify

Code

const promisify = func => (...args) =>
 new Promise((resolve, reject) =>
   func(...args, (err, result) => (err ? reject(err) : resolve(result)))
 );

Example

const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2s

Creates a function that invokes the provided function with its arguments arranged according to the specified indexes.

Use Array.prototype.map() to reorder arguments based on indexes in combination with the spread operator (...) to pass the transformed arguments to fn.

Code

const rearg = (fn, indexes) => (...args) => fn(...indexes.map(i => args[i]));

Example

var rearged = rearg(
 function(a, b, c) {
   return [a, b, c];
 },
 [2, 0, 1]
);
rearged('b', 'c', 'a'); // ['a', 'b', 'c']

Takes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.

Use closures and the spread operator (...) to map the array of arguments to the inputs of the function.

Code

const spreadOver = fn => argsArr => fn(...argsArr);

Example

const arrayMax = spreadOver(Math.max);
arrayMax([1, 2, 3]); // 3

Creates a function that accepts up to one argument, ignoring any additional arguments.

Call the provided function, fn, with just the first argument given.

Code

const unary = fn => val => fn(val);

Example

['6', '8', '10'].map(unary(parseInt)); // [6, 8, 10]

at res quokka.js:1664:0

Converts the given array elements into <li> tags and appends them to the list of the given id.

Use Array.prototype.map(), document.querySelector(), and an anonymous inner closure to create a list of html tags.

Code

const arrayToHtmlList = (arr, listID) =>
 (el => (
   (el = document.querySelector('#' + listID)),
   (el.innerHTML += arr.map(item => `<li>${item}</li>`).join(''))
 ))();

Example

arrayToHtmlList(['item 1', 'item 2'], 'myListID');

Returns true if the bottom of the page is visible, false otherwise.

Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.

Code

const bottomVisible = () =>
 document.documentElement.clientHeight + window.scrollY >=
 (document.documentElement.scrollHeight || document.documentElement.clientHeight);

Example

bottomVisible(); // true

⚠️ NOTICE: The same functionality can be easily implemented by using the new asynchronous Clipboard API, which is still experimental but should be used in the future instead of this snippet. Find out more about it here.

Copy a string to the clipboard. Only works as a result of user action (i.e. inside a click event listener).

Create a new <textarea> element, fill it with the supplied data and add it to the HTML document. Use Selection.getRangeAt()to store the selected range (if any). Use document.execCommand('copy') to copy to the clipboard. Remove the <textarea> element from the HTML document. Finally, use Selection().addRange() to recover the original selected range (if any).

Code

const copyToClipboard = str => {
 const el = document.createElement('textarea');
 el.value = str;
 el.setAttribute('readonly', '');
 el.style.position = 'absolute';
 el.style.left = '-9999px';
 document.body.appendChild(el);
 const selected =
   document.getSelection().rangeCount > 0 ? document.getSelection().getRangeAt(0) : false;
 el.select();
 document.execCommand('copy');
 document.body.removeChild(el);
 if (selected) {
   document.getSelection().removeAllRanges();
   document.getSelection().addRange(selected);
 }
};

Example

copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard.

Creates a counter with the specified range, step and duration for the specified selector.

Check if step has the proper sign and change it accordingly. Use setInterval() in combination with Math.abs() and Math.floor() to calculate the time between each new text draw. Use document.querySelector().innerHTML to update the value of the selected element. Omit the fourth parameter, step, to use a default step of 1. Omit the fifth parameter, duration, to use a default duration of 2000ms.

Code

const counter = (selector, start, end, step = 1, duration = 2000) => {
 let current = start,
   _step = (end - start) * step < 0 ? -step : step,
   timer = setInterval(() => {
     current += _step;
     document.querySelector(selector).innerHTML = current;
     if (current >= end) document.querySelector(selector).innerHTML = end;
     if (current >= end) clearInterval(timer);
   }, Math.abs(Math.floor(duration / (end - start))));
 return timer;
};

Example

counter('#my-id', 1, 1000, 5, 2000); // Creates a 2-second timer for the element with id="my-id"

Creates an element from a string (without appending it to the document).

If the given string contains multiple elements, only the first one will be returned.

Use document.createElement() to create a new element. Set its innerHTML to the string supplied as the argument. Use ParentNode.firstElementChild to return the element version of the string.

Code

const createElement = str => {
 const el = document.createElement('div');
 el.innerHTML = str;
 return el.firstElementChild;
};

Example

const el = createElement(
 `<div class="container">
   <p>Hello!</p>
 </div>`
);
console.log(el.className); // 'container'

Creates a pub/sub (publish–subscribe) event hub with emit, on, and off methods.

Use Object.create(null) to create an empty hub object that does not inherit properties from Object.prototype. For emit, resolve the array of handlers based on the event argument and then run each one with Array.prototype.forEach() by passing in the data as an argument. For on, create an array for the event if it does not yet exist, then use Array.prototype.push() to add the handler to the array. For off, use Array.prototype.findIndex() to find the index of the handler in the event array and remove it using Array.prototype.splice().

Code

const createEventHub = () => ({
 hub: Object.create(null),
 emit(event, data) {
   (this.hub[event] || []).forEach(handler => handler(data));
 },
 on(event, handler) {
   if (!this.hub[event]) this.hub[event] = [];
   this.hub[event].push(handler);
 },
 off(event, handler) {
   const i = (this.hub[event] || []).findIndex(h => h === handler);
   if (i > -1) this.hub[event].splice(i, 1);
 }
});

Example

const handler = data => console.log(data);
const hub = createEventHub();
let increment = 0;

// Subscribe: listen for different types of events
hub.on('message', handler);
hub.on('message', () => console.log('Message event fired'));
hub.on('increment', () => increment++);

// Publish: emit events to invoke all handlers subscribed to them, passing the data to them as an argument
hub.emit('message', 'hello world'); // logs 'hello world' and 'Message event fired'
hub.emit('message', { hello: 'world' }); // logs the object and 'Message event fired'
hub.emit('increment'); // `increment` variable is now 1

// Unsubscribe: stop a specific handler from listening to the 'message' event
hub.off('message', handler);

Returns the current URL.

Use window.location.href to get current URL.

Code

const currentURL = () => window.location.href;

Example

currentURL(); // 'https://google.com'

Detects wether the website is being opened in a mobile device or a desktop/laptop.

Use a regular expression to test the navigator.userAgent property to figure out if the device is a mobile device or a desktop/laptop.

Code

const detectDeviceType = () =>
 /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
   ? 'Mobile'
   : 'Desktop';

Example

detectDeviceType(); // "Mobile" or "Desktop"

Returns true if the parent element contains the child element, false otherwise.

Check that parent is not the same element as child, use parent.contains(child) to check if the parent element contains the child element.

Code

const elementContains = (parent, child) => parent !== child && parent.contains(child);

Example

elementContains(document.querySelector('head'), document.querySelector('title')); // true
elementContains(document.querySelector('body'), document.querySelector('body')); // false

Returns true if the element specified is visible in the viewport, false otherwise.

Use Element.getBoundingClientRect() and the window.inner(Width|Height) values to determine if a given element is visible in the viewport. Omit the second argument to determine if the element is entirely visible, or specify true to determine if it is partially visible.

Code

const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
 const { top, left, bottom, right } = el.getBoundingClientRect();
 const { innerHeight, innerWidth } = window;
 return partiallyVisible
   ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
       ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
   : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};

Example

// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
elementIsVisibleInViewport(el); // false - (not fully visible)
elementIsVisibleInViewport(el, true); // true - (partially visible)

Returns the scroll position of the current page.

Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop. You can omit el to use a default value of window.

Code

const getScrollPosition = (el = window) => ({
 x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
 y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});

Example

getScrollPosition(); // {x: 0, y: 200}

Returns the value of a CSS rule for the specified element.

Use Window.getComputedStyle() to get the value of the CSS rule for the specified element.

Code

const getStyle = (el, ruleName) => getComputedStyle(el)[ruleName];

Example

getStyle(document.querySelector('p'), 'font-size'); // '16px'

Returns true if the element has the specified class, false otherwise.

Use element.classList.contains() to check if the element has the specified class.

Code

const hasClass = (el, className) => el.classList.contains(className);

Example

hasClass(document.querySelector('p.special'), 'special'); // true

Creates a hash for a value using the SHA-256 algorithm. Returns a promise.

Use the SubtleCrypto API to create a hash for the given value.

Code

const hashBrowser = val =>
 crypto.subtle.digest('SHA-256', new TextEncoder('utf-8').encode(val)).then(h => {
   let hexes = [],
     view = new DataView(h);
   for (let i = 0; i < view.byteLength; i += 4)
     hexes.push(('00000000' + view.getUint32(i).toString(16)).slice(-8));
   return hexes.join('');
 });

Example

hashBrowser(JSON.stringify({ a: 'a', b: [1, 2, 3, 4], foo: { c: 'bar' } })).then(console.log); // '04aa106279f5977f59f9067fa9712afc4aedc6f5862a8defc34552d8c7206393'

Hides all the elements specified.

Use NodeList.prototype.forEach() to apply display: none to each element specified.

Code

const hide = els => els.forEach(e => (e.style.display = 'none'));

Example

hide(document.querySelectorAll('img')); // Hides all <img> elements on the page

Redirects the page to HTTPS if its currently in HTTP. Also, pressing the back button doesn't take it back to the HTTP page as its replaced in the history.

Use location.protocol to get the protocol currently being used. If it's not HTTPS, use location.replace() to replace the existing page with the HTTPS version of the page. Use location.href to get the full address, split it with String.prototype.split() and remove the protocol part of the URL.

Code

const httpsRedirect = () => {
 if (location.protocol !== 'https:') location.replace('https://' + location.href.split('//')[1]);
};

Example

httpsRedirect(); // If you are on http://mydomain.com, you are redirected to https://mydomain.com

Inserts an HTML string after the end of the specified element.

Use el.insertAdjacentHTML() with a position of 'afterend' to parse htmlString and insert it after the end of el.

Code

const insertAfter = (el, htmlString) => el.insertAdjacentHTML('afterend', htmlString);

Example

insertAfter(document.getElementById('myId'), '<p>after</p>'); // <div id="myId">...</div> <p>after</p>

Inserts an HTML string before the start of the specified element.

Use el.insertAdjacentHTML() with a position of 'beforebegin' to parse htmlString and insert it before the start of el.

Code

const insertBefore = (el, htmlString) => el.insertAdjacentHTML('beforebegin', htmlString);

Example

insertBefore(document.getElementById('myId'), '<p>before</p>'); // <p>before</p> <div id="myId">...</div>

Returns true if the browser tab of the page is focused, false otherwise.

Use the Document.hidden property, introduced by the Page Visibility API to check if the browser tab of the page is visible or hidden.

Code

const isBrowserTabFocused = () => !document.hidden;

Example

isBrowserTabFocused(); // true

Converts a NodeList to an array.

Use spread operator inside new array to convert a NodeList to an array.

Code

const nodeListToArray = nodeList => [...nodeList];

Example

nodeListToArray(document.childNodes); // [ <!DOCTYPE html>, html ]

Returns a new MutationObserver and runs the provided callback for each mutation on the specified element.

Use a MutationObserver to observe mutations on the given element. Use Array.prototype.forEach() to run the callback for each mutation that is observed. Omit the third argument, options, to use the default options (all true).

Code

const observeMutations = (element, callback, options) => {
 const observer = new MutationObserver(mutations => mutations.forEach(m => callback(m)));
 observer.observe(
   element,
   Object.assign(
     {
       childList: true,
       attributes: true,
       attributeOldValue: true,
       characterData: true,
       characterDataOldValue: true,
       subtree: true
     },
     options
   )
 );
 return observer;
};

Example

const obs = observeMutations(document, console.log); // Logs all mutations that happen on the page
obs.disconnect(); // Disconnects the observer and stops logging mutations on the page

Removes an event listener from an element.

Use EventTarget.removeEventListener() to remove an event listener from an element. Omit the fourth argument opts to use false or specify it based on the options used when the event listener was added.

Code

const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts);

Example

const fn = () => console.log('!');
document.body.addEventListener('click', fn);
off(document.body, 'click', fn); // no longer logs '!' upon clicking on the page

Adds an event listener to an element with the ability to use event delegation.

Use EventTarget.addEventListener() to add an event listener to an element. If there is a target property supplied to the options object, ensure the event target matches the target specified and then invoke the callback by supplying the correct this context. Returns a reference to the custom delegator function, in order to be possible to use with off. Omit opts to default to non-delegation behavior and event bubbling.

Code

const on = (el, evt, fn, opts = {}) => {
 const delegatorFn = e => e.target.matches(opts.target) && fn.call(e.target, e);
 el.addEventListener(evt, opts.target ? delegatorFn : fn, opts.options || false);
 if (opts.target) return delegatorFn;
};

Example

const fn = () => console.log('!');
on(document.body, 'click', fn); // logs '!' upon clicking the body
on(document.body, 'click', fn, { target: 'p' }); // logs '!' upon clicking a `p` element child of the body
on(document.body, 'click', fn, { options: true }); // use capturing instead of bubbling

Run the callback whenever the user input type changes (mouse or touch). Useful for enabling/disabling code depending on the input device. This process is dynamic and works with hybrid devices (e.g. touchscreen laptops).

Use two event listeners. Assume mouse input initially and bind a touchstart event listener to the document. On touchstart, add a mousemove event listener to listen for two consecutive mousemove events firing within 20ms, using performance.now(). Run the callback with the input type as an argument in either of these situations.

Code

const onUserInputChange = callback => {
 let type = 'mouse',
   lastTime = 0;
 const mousemoveHandler = () => {
   const now = performance.now();
   if (now - lastTime < 20)
     (type = 'mouse'), callback(type), document.removeEventListener('mousemove', mousemoveHandler);
   lastTime = now;
 };
 document.addEventListener('touchstart', () => {
   if (type === 'touch') return;
   (type = 'touch'), callback(type), document.addEventListener('mousemove', mousemoveHandler);
 });
};

Example

onUserInputChange(type => {
 console.log('The user is now using', type, 'as an input method.');
});

Returns the prefixed version (if necessary) of a CSS property that the browser supports.

Use Array.prototype.findIndex() on an array of vendor prefix strings to test if document.body has one of them defined in its CSSStyleDeclaration object, otherwise return null. Use String.prototype.charAt() and String.prototype.toUpperCase() to capitalize the property, which will be appended to the vendor prefix string.

Code

const prefix = prop => {
 const capitalizedProp = prop.charAt(0).toUpperCase() + prop.slice(1);
 const prefixes = ['', 'webkit', 'moz', 'ms', 'o'];
 const i = prefixes.findIndex(
   prefix => typeof document.body.style[prefix ? prefix + capitalizedProp : prop] !== 'undefined'
 );
 return i !== -1 ? (i === 0 ? prop : prefixes[i] + capitalizedProp) : null;
};

Example

prefix('appearance'); // 'appearance' on a supported browser, otherwise 'webkitAppearance', 'mozAppearance', 'msAppearance' or 'oAppearance'

Invokes the provided callback on each animation frame.

Use recursion. Provided that running is true, continue invoking window.requestAnimationFrame() which invokes the provided callback. Return an object with two methods start and stop to allow manual control of the recording. Omit the second argument, autoStart, to implicitly call start when the function is invoked.

Code

const recordAnimationFrames = (callback, autoStart = true) => {
 let running = true,
   raf;
 const stop = () => {
   running = false;
   cancelAnimationFrame(raf);
 };
 const start = () => {
   running = true;
   run();
 };
 const run = () => {
   raf = requestAnimationFrame(() => {
     callback();
     if (running) run();
   });
 };
 if (autoStart) start();
 return { start, stop };
};

Example

const cb = () => console.log('Animation frame fired');
const recorder = recordAnimationFrames(cb); // logs 'Animation frame fired' on each animation frame
recorder.stop(); // stops logging
recorder.start(); // starts again
const recorder2 = recordAnimationFrames(cb, false); // `start` needs to be explicitly called to begin recording frames

Redirects to a specified URL.

Use window.location.href or window.location.replace() to redirect to url. Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).

Code

const redirect = (url, asLink = true) =>
 asLink ? (window.location.href = url) : window.location.replace(url);

Example

redirect('https://google.com');

Runs a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI.

Create a new Worker using a Blob object URL, the contents of which should be the stringified version of the supplied function. Immediately post the return value of calling the function back. Return a promise, listening for onmessage and onerror events and resolving the data posted back from the worker, or throwing an error.

Code

const runAsync = fn => {
 const worker = new Worker(
   URL.createObjectURL(new Blob([`postMessage((${fn})());`]), {
     type: 'application/javascript; charset=utf-8'
   })
 );
 return new Promise((res, rej) => {
   worker.onmessage = ({ data }) => {
     res(data), worker.terminate();
   };
   worker.onerror = err => {
     rej(err), worker.terminate();
   };
 });
};

Example

const longRunningFunction = () => {
 let result = 0;
 for (let i = 0; i < 1000; i++) {
   for (let j = 0; j < 700; j++) {
     for (let k = 0; k < 300; k++) {
       result = result + i + j + k;
     }
   }
 }
 return result;
};
/*
 NOTE: Since the function is running in a different context, closures are not supported.
 The function supplied to `runAsync` gets stringified, so everything becomes literal.
 All variables and functions must be defined inside.
*/
runAsync(longRunningFunction).then(console.log); // 209685000000
runAsync(() => 10 ** 3).then(console.log); // 1000
let outsideVariable = 50;
runAsync(() => typeof outsideVariable).then(console.log); // 'undefined'

Smooth-scrolls to the top of the page.

Get distance from top using document.documentElement.scrollTop or document.body.scrollTop. Scroll by a fraction of the distance from the top. Use window.requestAnimationFrame() to animate the scrolling.

Code

const scrollToTop = () => {
 const c = document.documentElement.scrollTop || document.body.scrollTop;
 if (c > 0) {
   window.requestAnimationFrame(scrollToTop);
   window.scrollTo(0, c - c / 8);
 }
};

Example

scrollToTop();

Sets the value of a CSS rule for the specified element.

Use element.style to set the value of the CSS rule for the specified element to val.

Code

const setStyle = (el, ruleName, val) => (el.style[ruleName] = val);

Example

setStyle(document.querySelector('p'), 'font-size', '20px'); // The first <p> element on the page will have a font-size of 20px

Shows all the elements specified.

Use the spread operator (...) and Array.prototype.forEach() to clear the display property for each element specified.

Code

const show = (...el) => [...el].forEach(e => (e.style.display = ''));

Example

show(...document.querySelectorAll('img')); // Shows all <img> elements on the page

Smoothly scrolls the element on which it's called into the visible area of the browser window.

Use .scrollIntoView method to scroll the element. Pass { behavior: 'smooth' } to .scrollIntoView so it scrolls smoothly.

Code

const smoothScroll = element =>
 document.querySelector(element).scrollIntoView({
   behavior: 'smooth'
 });

Example

smoothScroll('#fooBar'); // scrolls smoothly to the element with the id fooBar
smoothScroll('.fooBar'); // scrolls smoothly to the first element with a class of fooBar

Toggle a class for an element.

Use element.classList.toggle() to toggle the specified class for the element.

Code

const toggleClass = (el, className) => el.classList.toggle(className);

Example

toggleClass(document.querySelector('p.special'), 'special'); // The paragraph will not have the 'special' class anymore

Triggers a specific event on a given element, optionally passing custom data.

Use new CustomEvent() to create an event from the specified eventType and details. Use el.dispatchEvent() to trigger the newly created event on the given element. Omit the third argument, detail, if you do not want to pass custom data to the triggered event.

Code

const triggerEvent = (el, eventType, detail = undefined) =>
 el.dispatchEvent(new CustomEvent(eventType, { detail: detail }));

Example

triggerEvent(document.getElementById('myId'), 'click');
triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });

Generates a UUID in a browser.

Use crypto API to generate a UUID, compliant with RFC4122 version 4.

Code

const UUIDGeneratorBrowser = () =>
 ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
   (c ^ (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))).toString(16)
 );

Example

UUIDGeneratorBrowser(); // '7982fcfe-5721-4632-bede-6000885be57d'

at res quokka.js:1664:0

Gets the day of the year from a Date object.

Use new Date() and Date.prototype.getFullYear() to get the first day of the year as a Date object, subtract it from the provided date and divide with the milliseconds in each day to get the result. Use Math.floor() to appropriately round the resulting day count to an integer.

Code

const dayOfYear = date =>
 Math.floor((date - new Date(date.getFullYear(), 0, 0)) / 1000 / 60 / 60 / 24);

Example

dayOfYear(new Date()); // 272

Returns the human readable format of the given number of milliseconds.

Divide ms with the appropriate values to obtain the appropriate values for day, hour, minute, second and millisecond. Use Object.entries() with Array.prototype.filter() to keep only non-zero values. Use Array.prototype.map() to create the string for each value, pluralizing appropriately. Use String.prototype.join(', ') to combine the values into a string.

Code

const formatDuration = ms => {
 if (ms < 0) ms = -ms;
 const time = {
   day: Math.floor(ms / 86400000),
   hour: Math.floor(ms / 3600000) % 24,
   minute: Math.floor(ms / 60000) % 60,
   second: Math.floor(ms / 1000) % 60,
   millisecond: Math.floor(ms) % 1000
 };
 return Object.entries(time)
   .filter(val => val[1] !== 0)
   .map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`)
   .join(', ');
};

Example

formatDuration(1001); // '1 second, 1 millisecond'
formatDuration(34325055574); // '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'

Returns a string of the form HH:MM:SS from a Date object.

Use Date.prototype.toString() and String.prototype.slice() to get the HH:MM:SS part of a given Date object.

Code

const getColonTimeFromDate = date => date.toTimeString().slice(0, 8);

Example

getColonTimeFromDate(new Date()); // "08:38:00"

Returns the difference (in days) between two dates.

Calculate the difference (in days) between two Date objects.

Code

const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
 (dateFinal - dateInitial) / (1000 * 3600 * 24);

Example

getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9

Converts an integer to a suffixed string, adding am or pm based on its value.

Use the modulo operator (%) and conditional checks to transform an integer to a stringified 12-hour format with meridiem suffix.

Code

const getMeridiemSuffixOfInteger = num =>
 num === 0 || num === 24
   ? 12 + 'am'
   : num === 12
     ? 12 + 'pm'
     : num < 12
       ? (num % 12) + 'am'
       : (num % 12) + 'pm';

Example

getMeridiemSuffixOfInteger(0); // "12am"
getMeridiemSuffixOfInteger(11); // "11am"
getMeridiemSuffixOfInteger(13); // "1pm"
getMeridiemSuffixOfInteger(25); // "1pm"

Check if a date is after another date.

Use the greater than operator (>) to check if the first date comes after the second one.

Code

const isAfterDate = (dateA, dateB) => dateA > dateB;

Example

isAfterDate(new Date(2010, 10, 21), new Date(2010, 10, 20)); // true

Check if a date is before another date.

Use the less than operator (<) to check if the first date comes before the second one.

Code

const isBeforeDate = (dateA, dateB) => dateA < dateB;

Example

isBeforeDate(new Date(2010, 10, 20), new Date(2010, 10, 21)); // true

Check if a date is the same as another date.

Use Date.prototype.toISOString() and strict equality checking (===) to check if the first date is the same as the second one.

Code

const isSameDate = (dateA, dateB) => dateA.toISOString() === dateB.toISOString();

Example

isSameDate(new Date(2010, 10, 20), new Date(2010, 10, 20)); // true

Returns the maximum of the given dates.

Use Math.max.apply() to find the maximum date value, new Date() to convert it to a Date object.

Code

const maxDate = (...dates) => new Date(Math.max.apply(null, ...dates));

Example

const array = [
 new Date(2017, 4, 13),
 new Date(2018, 2, 12),
 new Date(2016, 0, 10),
 new Date(2016, 0, 9)
];
maxDate(array); // 2018-03-11T22:00:00.000Z

Returns the minimum of the given dates.

Use Math.min.apply() to find the minimum date value, new Date() to convert it to a Date object.

Code

const minDate = (...dates) => new Date(Math.min.apply(null, ...dates));

Example

const array = [
 new Date(2017, 4, 13),
 new Date(2018, 2, 12),
 new Date(2016, 0, 10),
 new Date(2016, 0, 9)
];
minDate(array); // 2016-01-08T22:00:00.000Z

Results in a string representation of tomorrow's date.

Use new Date() to get today's date, adding one day using Date.getDate() and Date.setDate(), and converting the Date object to a string.

Code

const tomorrow = (long = false) => {
 let t = new Date();
 t.setDate(t.getDate() + 1);
 const ret = `${t.getFullYear()}-${String(t.getMonth() + 1).padStart(2, '0')}-${String(
   t.getDate()
 ).padStart(2, '0')}`;
 return !long ? ret : `${ret}T00:00:00`;
};

Example

tomorrow(); // 2017-12-27 (if current date is 2017-12-26)
tomorrow(true); // 2017-12-27T00:00:00 (if current date is 2017-12-26)

at res quokka.js:1664:0

Attempts to invoke a function with the provided arguments, returning either the result or the caught error object.

Use a try... catch block to return either the result of the function or an appropriate error.

Code

const attempt = (fn, ...args) => {
 try {
   return fn(...args);
 } catch (e) {
   return e instanceof Error ? e : new Error(e);
 }
};

Example

var elements = attempt(function(selector) {
 return document.querySelectorAll(selector);
}, '>_>');
if (elements instanceof Error) elements = []; // elements = []

Creates a function that invokes fn with a given context, optionally adding any additional supplied parameters to the beginning of the arguments.

Return a function that uses Function.prototype.apply() to apply the given context to fn. Use Array.prototype.concat() to prepend any additional supplied parameters to the arguments.

Code

const bind = (fn, context, ...boundArgs) => (...args) => fn.apply(context, [...boundArgs, ...args]);

Example

function greet(greeting, punctuation) {
 return greeting + ' ' + this.user + punctuation;
}
const freddy = { user: 'fred' };
const freddyBound = bind(greet, freddy);
console.log(freddyBound('hi', '!')); // 'hi fred!'

Creates a function that invokes the method at a given key of an object, optionally adding any additional supplied parameters to the beginning of the arguments.

Return a function that uses Function.prototype.apply() to bind context[fn] to context. Use the spread operator (...) to prepend any additional supplied parameters to the arguments.

Code

const bindKey = (context, fn, ...boundArgs) => (...args) =>
 context[fn].apply(context, [...boundArgs, ...args]);

Example

const freddy = {
 user: 'fred',
 greet: function(greeting, punctuation) {
   return greeting + ' ' + this.user + punctuation;
 }
};
const freddyBound = bindKey(freddy, 'greet');
console.log(freddyBound('hi', '!')); // 'hi fred!'

Chains asynchronous functions.

Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.

Code

const chainAsync = fns => {
 let curr = 0;
 const next = () => fns[curr++](next);
 next();
};

Example

chainAsync([
 next => {
   console.log('0 seconds');
   setTimeout(next, 1000);
 },
 next => {
   console.log('1 second');
 }
]);

Performs right-to-left function composition.

Use Array.prototype.reduce() to perform right-to-left function composition. The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.

Code

const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));

Example

const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = compose(
 add5,
 multiply
);
multiplyAndAdd5(5, 2); // 15

Performs left-to-right function composition.

Use Array.prototype.reduce() to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.

Code

const composeRight = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));

Example

const add = (x, y) => x + y;
const square = x => x * x;
const addAndSquare = composeRight(add, square);
addAndSquare(1, 2); // 9

Accepts a converging function and a list of branching functions and returns a function that applies each branching function to the arguments and the results of the branching functions are passed as arguments to the converging function.

Use Array.prototype.map() and Function.prototype.apply() to apply each function to the given arguments. Use the spread operator (...) to call coverger with the results of all other functions.

Code

const converge = (converger, fns) => (...args) => converger(...fns.map(fn => fn.apply(null, args)));

Example

const average = converge((a, b) => a / b, [
 arr => arr.reduce((a, v) => a + v, 0),
 arr => arr.length
]);
average([1, 2, 3, 4, 5, 6, 7]); // 4

Curries a function.

Use recursion. If the number of provided arguments (args) is sufficient, call the passed function fn. Otherwise, return a curried function fn that expects the rest of the arguments. If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.

Code

const curry = (fn, arity = fn.length, ...args) =>
 arity <= args.length ? fn(...args) : curry.bind(null, fn, arity, ...args);

Example

curry(Math.pow)(2)(10); // 1024
curry(Math.min, 3)(10)(50)(2); // 2

Creates a debounced function that delays invoking the provided function until at least ms milliseconds have elapsed since the last time it was invoked.

Each time the debounced function is invoked, clear the current pending timeout with clearTimeout() and use setTimeout() to create a new timeout that delays invoking the function until at least ms milliseconds has elapsed. Use Function.prototype.apply() to apply the this context to the function and provide the necessary arguments. Omit the second argument, ms, to set the timeout at a default of 0 ms.

Code

const debounce = (fn, ms = 0) => {
 let timeoutId;
 return function(...args) {
   clearTimeout(timeoutId);
   timeoutId = setTimeout(() => fn.apply(this, args), ms);
 };
};

Example

window.addEventListener(
 'resize',
 debounce(() => {
   console.log(window.innerWidth);
   console.log(window.innerHeight);
 }, 250)
); // Will log the window dimensions at most every 250ms

Defers invoking a function until the current call stack has cleared.

Use setTimeout() with a timeout of 1ms to add a new event to the browser event queue and allow the rendering engine to complete its work. Use the spread (...) operator to supply the function with an arbitrary number of arguments.

Code

const defer = (fn, ...args) => setTimeout(fn, 1, ...args);

Example

// Example A:
defer(console.log, 'a'), console.log('b'); // logs 'b' then 'a'

// Example B:
document.querySelector('#someElement').innerHTML = 'Hello';
longRunningFunction(); //Browser will not update the HTML until this has finished
defer(longRunningFunction); // Browser will update the HTML then run the function

Invokes the provided function after wait milliseconds.

Use setTimeout() to delay execution of fn. Use the spread (...) operator to supply the function with an arbitrary number of arguments.

Code

const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);

Example

delay(
 function(text) {
   console.log(text);
 },
 1000,
 'later'
); // Logs 'later' after one second.

Logs the name of a function.

Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.

Code

const functionName = fn => (console.debug(fn.name), fn);

Example

functionName(Math.max); // max (logged in debug channel of console)

Returns the number of times a function executed per second.

hz is the unit for hertz, the unit of frequency defined as one cycle per second.

Use performance.now() to get the difference in milliseconds before and after the iteration loop to calculate the time elapsed executing the function iterations times. Return the number of cycles per second by converting milliseconds to seconds and dividing it by the time elapsed. Omit the second argument, iterations, to use the default of 100 iterations.

Code

const hz = (fn, iterations = 100) => {
 const before = performance.now();
 for (let i = 0; i < iterations; i++) fn();
 return (1000 * iterations) / (performance.now() - before);
};

Example

// 10,000 element array
const numbers = Array(10000)
 .fill()
 .map((_, i) => i);

// Test functions with the same goal: sum up the elements in the array
const sumReduce = () => numbers.reduce((acc, n) => acc + n, 0);
const sumForLoop = () => {
 let sum = 0;
 for (let i = 0; i < numbers.length; i++) sum += numbers[i];
 return sum;
};

// `sumForLoop` is nearly 10 times faster
Math.round(hz(sumReduce)); // 572
Math.round(hz(sumForLoop)); // 4784

Returns the memoized (cached) function.

Create an empty cache by instantiating a new Map object. Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not. The function keyword must be used in order to allow the memoized function to have its this context changed if necessary. Allow access to the cache by setting it as a property on the returned function.

Code

const memoize = fn => {
 const cache = new Map();
 const cached = function(val) {
   return cache.has(val) ? cache.get(val) : cache.set(val, fn.call(this, val)) && cache.get(val);
 };
 cached.cache = cache;
 return cached;
};

Example

// See the `anagrams` snippet.
const anagramsCached = memoize(anagrams);
anagramsCached('javascript'); // takes a long time
anagramsCached('javascript'); // returns virtually instantly since it's now cached
console.log(anagramsCached.cache); // The cached anagrams map

Negates a predicate function.

Take a predicate function and apply the not operator (!) to it with its arguments.

Code

const negate = func => (...args) => !func(...args);

Example

[1, 2, 3, 4, 5, 6].filter(negate(n => n % 2 === 0)); // [ 1, 3, 5 ]

Ensures a function is called only once.

Utilizing a closure, use a flag, called, and set it to true once the function is called for the first time, preventing it from being called again. In order to allow the function to have its this context changed (such as in an event listener), the function keyword must be used, and the supplied function must have the context applied. Allow the function to be supplied with an arbitrary number of arguments using the rest/spread (...) operator.

Code

const once = fn => {
 let called = false;
 return function(...args) {
   if (called) return;
   called = true;
   return fn.apply(this, args);
 };
};

Example

const startApp = function(event) {
 console.log(this, event); // document.body, MouseEvent
};
document.body.addEventListener('click', once(startApp)); // only runs `startApp` once upon click

Creates a function that invokes fn with partials prepended to the arguments it receives.

Use the spread operator (...) to prepend partials to the list of arguments of fn.

Code

const partial = (fn, ...partials) => (...args) => fn(...partials, ...args);

Example

const greet = (greeting, name) => greeting + ' ' + name + '!';
const greetHello = partial(greet, 'Hello');
greetHello('John'); // 'Hello John!'

Creates a function that invokes fn with partials appended to the arguments it receives.

Use the spread operator (...) to append partials to the list of arguments of fn.

Code

const partialRight = (fn, ...partials) => (...args) => fn(...args, ...partials);

Example

const greet = (greeting, name) => greeting + ' ' + name + '!';
const greetJohn = partialRight(greet, 'John');
greetJohn('Hello'); // 'Hello John!'

Runs an array of promises in series.

Use Array.prototype.reduce() to create a promise chain, where each promise returns the next promise when resolved.

Code

const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());

Example

const delay = d => new Promise(r => setTimeout(r, d));
runPromisesInSeries([() => delay(1000), () => delay(2000)]); // Executes each promise sequentially, taking a total of 3 seconds to complete

Delays the execution of an asynchronous function.

Delay executing part of an async function, by putting it to sleep, returning a Promise.

Code

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));

Example

async function sleepyWork() {
 console.log("I'm going to sleep for 1 second.");
 await sleep(1000);
 console.log('I woke up after 1 second.');
}

Creates a throttled function that only invokes the provided function at most once per every wait milliseconds

Use setTimeout() and clearTimeout() to throttle the given method, fn. Use Function.prototype.apply() to apply the this context to the function and provide the necessary arguments. Use Date.now() to keep track of the last time the throttled function was invoked. Omit the second argument, wait, to set the timeout at a default of 0 ms.

Code

const throttle = (fn, wait) => {
 let inThrottle, lastFn, lastTime;
 return function() {
   const context = this,
     args = arguments;
   if (!inThrottle) {
     fn.apply(context, args);
     lastTime = Date.now();
     inThrottle = true;
   } else {
     clearTimeout(lastFn);
     lastFn = setTimeout(function() {
       if (Date.now() - lastTime >= wait) {
         fn.apply(context, args);
         lastTime = Date.now();
       }
     }, wait - (Date.now() - lastTime));
   }
 };
};

Example

window.addEventListener(
 'resize',
 throttle(function(evt) {
   console.log(window.innerWidth);
   console.log(window.innerHeight);
 }, 250)
); // Will log the window dimensions at most every 250ms

Iterates over a callback n times

Use Function.call() to call fn n times or until it returns false. Omit the last argument, context, to use an undefined object (or the global object in non-strict mode).

Code

const times = (n, fn, context = undefined) => {
 let i = 0;
 while (fn.call(context, i) !== false && ++i < n) {}
};

Example

var output = '';
times(5, i => (output += i));
console.log(output); // 01234

Uncurries a function up to depth n.

Return a variadic function. Use Array.prototype.reduce() on the provided arguments to call each subsequent curry level of the function. If the length of the provided arguments is less than n throw an error. Otherwise, call fn with the proper amount of arguments, using Array.prototype.slice(0, n). Omit the second argument, n, to uncurry up to depth 1.

Code

const uncurry = (fn, n = 1) => (...args) => {
 const next = acc => args => args.reduce((x, y) => x(y), acc);
 if (n > args.length) throw new RangeError('Arguments too few!');
 return next(fn)(args.slice(0, n));
};

Example

const add = x => y => z => x + y + z;
const uncurriedAdd = uncurry(add, 3);
uncurriedAdd(1, 2, 3); // 6

Builds an array, using an iterator function and an initial seed value.

Use a while loop and Array.prototype.push() to call the function repeatedly until it returns false. The iterator function accepts one argument (seed) and must always return an array with two elements ([value, nextSeed]) or false to terminate.

Code

const unfold = (fn, seed) => {
 let result = [],
   val = [null, seed];
 while ((val = fn(val[1]))) result.push(val[0]);
 return result;
};

Example

var f = n => (n > 50 ? false : [-n, n + 10]);
unfold(f, 10); // [-10, -20, -30, -40, -50]

Tests a value, x, against a predicate function. If true, return fn(x). Else, return x.

Return a function expecting a single value, x, that returns the appropriate value based on pred.

Code

const when = (pred, whenTrue) => x => (pred(x) ? whenTrue(x) : x);

Example

const doubleEvenNumbers = when(x => x % 2 === 0, x => x * 2);
doubleEvenNumbers(2); // 4
doubleEvenNumbers(1); // 1

Checks if two numbers are approximately equal to each other.

Use Math.abs() to compare the absolute difference of the two values to epsilon. Omit the third parameter, epsilon, to use a default value of 0.001.

Code

const approximatelyEqual = (v1, v2, epsilon = 0.001) => Math.abs(v1 - v2) < epsilon;

Example

approximatelyEqual(Math.PI / 2.0, 1.5708); // true

Returns the average of two or more numbers.

Use Array.prototype.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.

Code

const average = (...nums) => nums.reduce((acc, val) => acc + val, 0) / nums.length;

Example

average(...[1, 2, 3]); // 2
average(1, 2, 3); // 2

Returns the average of an array, after mapping each element to a value using the provided function.

Use Array.prototype.map() to map each element to the value returned by fn, Array.prototype.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.

Code

const averageBy = (arr, fn) =>
 arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0) /
 arr.length;

Example

averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 5
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 5

Evaluates the binomial coefficient of two integers n and k.

Use Number.isNaN() to check if any of the two values is NaN. Check if k is less than 0, greater than or equal to n, equal to 1 or n - 1 and return the appropriate result. Check if n - k is less than k and switch their values accordingly. Loop from 2 through k and calculate the binomial coefficient. Use Math.round() to account for rounding errors in the calculation.

Code

const binomialCoefficient = (n, k) => {
 if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
 if (k < 0 || k > n) return 0;
 if (k === 0 || k === n) return 1;
 if (k === 1 || k === n - 1) return n;
 if (n - k < k) k = n - k;
 let res = n;
 for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
 return Math.round(res);
};

Example

binomialCoefficient(8, 2); // 28

Clamps num within the inclusive range specified by the boundary values a and b.

If num falls within the range, return num. Otherwise, return the nearest number in the range.

Code

const clampNumber = (num, a, b) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));

Example

clampNumber(2, 3, 5); // 3
clampNumber(1, -1, -5); // -1

Converts an angle from degrees to radians.

Use Math.PI and the degree to radian formula to convert the angle from degrees to radians.

Code

const degreesToRads = deg => (deg * Math.PI) / 180.0;

Example

degreesToRads(90.0); // ~1.5708

Converts a number to an array of digits.

Convert the number to a string, using the spread operator (...) to build an array. Use Array.prototype.map() and parseInt() to transform each value to an integer.

Code

const digitize = n => [...`${n}`].map(i => parseInt(i));

Example

digitize(123); // [1, 2, 3]

Returns the distance between two points.

Use Math.hypot() to calculate the Euclidean distance between two points.

Code

const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);

Example

distance(1, 1, 2, 3); // 2.23606797749979

Computes the new ratings between two or more opponents using the Elo rating system. It takes an array

of pre-ratings and returns an array containing post-ratings. The array should be ordered from best performer to worst performer (winner -> loser).

Use the exponent ** operator and math operators to compute the expected score (chance of winning). of each opponent and compute the new rating for each. Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion. Omit the second argument to use the default kFactor of 32.

Code

const elo = ([...ratings], kFactor = 32, selfRating) => {
 const [a, b] = ratings;
 const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400));
 const newRating = (rating, i) =>
   (selfRating || rating) + kFactor * (i - expectedScore(i ? a : b, i ? b : a));
 if (ratings.length === 2) {
   return [newRating(a, 1), newRating(b, 0)];
 }
 for (let i = 0, len = ratings.length; i < len; i++) {
   let j = i;
   while (j < len - 1) {
     j++;
     [ratings[i], ratings[j]] = elo([ratings[i], ratings[j]], kFactor);
   }
 }
 return ratings;
};

Example

// Standard 1v1s
elo([1200, 1200]); // [1216, 1184]
elo([1200, 1200], 64); // [1232, 1168]
// 4 player FFA, all same rank
elo([1200, 1200, 1200, 1200]).map(Math.round); // [1246, 1215, 1185, 1154]
/*
For teams, each rating can adjusted based on own team's average rating vs.
average rating of opposing team, with the score being added to their
own individual rating by supplying it as the third argument.
*/

Calculates the factorial of a number.

Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1. Throws an exception if n is a negative number.

Code

const factorial = n =>
 n < 0
   ? (() => {
       throw new TypeError('Negative numbers are not allowed!');
     })()
   : n <= 1
     ? 1
     : n * factorial(n - 1);

Example

factorial(6); // 720

Generates an array, containing the Fibonacci sequence, up until the nth term.

Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.prototype.reduce() to add values into the array, using the sum of the last two values, except for the first two.

Code

const fibonacci = n =>
 Array.from({ length: n }).reduce(
   (acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),
   []
 );

Example

fibonacci(6); // [0, 1, 1, 2, 3, 5]

Calculates the greatest common divisor between two or more numbers/arrays.

The inner _gcd function uses recursion. Base case is when y equals 0. In this case, return x. Otherwise, return the GCD of y and the remainder of the division x/y.

Code

const gcd = (...arr) => {
 const _gcd = (x, y) => (!y ? x : gcd(y, x % y));
 return [...arr].reduce((a, b) => _gcd(a, b));
};

Example

gcd(8, 36); // 4
gcd(...[12, 8, 32]); // 4

Initializes an array containing the numbers in the specified range where start and end are inclusive and the ratio between two terms is step.

Returns an error if step equals 1.

Use Array.from(), Math.log() and Math.floor() to create an array of the desired length, Array.prototype.map() to fill with the desired values in a range. Omit the second argument, start, to use a default value of 1. Omit the third argument, step, to use a default value of 2.

Code

const geometricProgression = (end, start = 1, step = 2) =>
 Array.from({ length: Math.floor(Math.log(end / start) / Math.log(step)) + 1 }).map(
   (v, i) => start * step ** i
 );

Example

geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 256]
geometricProgression(256, 3); // [3, 6, 12, 24, 48, 96, 192]
geometricProgression(256, 1, 4); // [1, 4, 16, 64, 256]

Calculates the Hamming distance between two values.

Use XOR operator (^) to find the bit difference between the two numbers, convert to a binary string using toString(2). Count and return the number of 1s in the string, using match(/1/g).

Code

const hammingDistance = (num1, num2) => ((num1 ^ num2).toString(2).match(/1/g) || '').length;

Example

hammingDistance(2, 3); // 1

Checks if the given number falls within the given range.

Use arithmetic comparison to check if the given number is in the specified range. If the second parameter, end, is not specified, the range is considered to be from 0 to start.

Code

const inRange = (n, start, end = null) => {
 if (end && start > end) [end, start] = [start, end];
 return end == null ? n >= 0 && n < start : n >= start && n < end;
};

Example

inRange(3, 2, 5); // true
inRange(3, 4); // true
inRange(2, 3, 5); // false
inRange(3, 2); // false

Checks if the first numeric argument is divisible by the second one.

Use the modulo operator (%) to check if the remainder is equal to 0.

Code

const isDivisible = (dividend, divisor) => dividend % divisor === 0;

Example

isDivisible(6, 3); // true

Returns true if the given number is even, false otherwise.

Checks whether a number is odd or even using the modulo (%) operator. Returns true if the number is even, false if the number is odd.

Code

const isEven = num => num % 2 === 0;

Example

isEven(3); // false

Checks if the provided integer is a prime number.

Check numbers from 2 to the square root of the given number. Return false if any of them divides the given number, else return true, unless the number is less than 2.

Code

const isPrime = num => {
 const boundary = Math.floor(Math.sqrt(num));
 for (var i = 2; i <= boundary; i++) if (num % i === 0) return false;
 return num >= 2;
};

Example

isPrime(11); // true

Returns the least common multiple of two or more numbers.

Use the greatest common divisor (GCD) formula and the fact that lcm(x,y) = x * y / gcd(x,y) to determine the least common multiple. The GCD formula uses recursion.

Code

const lcm = (...arr) => {
 const gcd = (x, y) => (!y ? x : gcd(y, x % y));
 const _lcm = (x, y) => (x * y) / gcd(x, y);
 return [...arr].reduce((a, b) => _lcm(a, b));
};

Example

lcm(12, 7); // 84
lcm(...[1, 3, 4, 5]); // 60

Implementation of the Luhn Algorithm used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc.

Use String.prototype.split(''), Array.prototype.reverse() and Array.prototype.map() in combination with parseInt() to obtain an array of digits. Use Array.prototype.splice(0,1) to obtain the last digit. Use Array.prototype.reduce() to implement the Luhn Algorithm. Return true if sum is divisible by 10, false otherwise.

Code

const luhnCheck = num => {
 let arr = (num + '')
   .split('')
   .reverse()
   .map(x => parseInt(x));
 let lastDigit = arr.splice(0, 1)[0];
 let sum = arr.reduce((acc, val, i) => (i % 2 !== 0 ? acc + val : acc + ((val * 2) % 9) || 9), 0);
 sum += lastDigit;
 return sum % 10 === 0;
};

Example

luhnCheck('4485275742308327'); // true
luhnCheck(6011329933655299); //  false
luhnCheck(123456789); // false

Returns the maximum value of an array, after mapping each element to a value using the provided function.

Use Array.prototype.map() to map each element to the value returned by fn, Math.max() to get the maximum value.

Code

const maxBy = (arr, fn) => Math.max(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));

Example

maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 8
maxBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 8

Returns the median of an array of numbers.

Find the middle of the array, use Array.prototype.sort() to sort the values. Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.

Code

const median = arr => {
 const mid = Math.floor(arr.length / 2),
   nums = [...arr].sort((a, b) => a - b);
 return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};

Example

median([5, 6, 50, 1, -5]); // 5

Returns the minimum value of an array, after mapping each element to a value using the provided function.

Use Array.prototype.map() to map each element to the value returned by fn, Math.min() to get the maximum value.

Code

const minBy = (arr, fn) => Math.min(...arr.map(typeof fn === 'function' ? fn : val => val[fn]));

Example

minBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 2
minBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 2

Uses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.

Use Array.prototype.reduce() to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.

Code

const percentile = (arr, val) =>
 (100 * arr.reduce((acc, v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0)) / arr.length;

Example

percentile([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 6); // 55

Returns the powerset of a given array of numbers.

Use Array.prototype.reduce() combined with Array.prototype.map() to iterate over elements and combine into an array containing all combinations.

Code

const powerset = arr => arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);

Example

powerset([1, 2]); // [[], [1], [2], [2, 1]]

Generates primes up to a given number, using the Sieve of Eratosthenes.

Generate an array from 2 to the given number. Use Array.prototype.filter() to filter out the values divisible by any number from 2 to the square root of the provided number.

Code

const primes = num => {
 let arr = Array.from({ length: num - 1 }).map((x, i) => i + 2),
   sqroot = Math.floor(Math.sqrt(num)),
   numsTillSqroot = Array.from({ length: sqroot - 1 }).map((x, i) => i + 2);
 numsTillSqroot.forEach(x => (arr = arr.filter(y => y % x !== 0 || y === x)));
 return arr;
};

Example

primes(10); // [2,3,5,7]

Converts an angle from radians to degrees.

Use Math.PI and the radian to degree formula to convert the angle from radians to degrees.

Code

const radsToDegrees = rad => (rad * 180.0) / Math.PI;

Example

radsToDegrees(Math.PI / 2); // 90

Returns an array of n random integers in the specified range.

Use Array.from() to create an empty array of the specific length, Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.

Code

const randomIntArrayInRange = (min, max, n = 1) =>
 Array.from({ length: n }, () => Math.floor(Math.random() * (max - min + 1)) + min);

Example

randomIntArrayInRange(12, 35, 10); // [ 34, 14, 27, 17, 30, 27, 20, 26, 21, 14 ]

Returns a random integer in the specified range.

Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.

Code

const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;

Example

randomIntegerInRange(0, 5); // 2

Returns a random number in the specified range.

Use Math.random() to generate a random value, map it to the desired range using multiplication.

Code

const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;

Example

randomNumberInRange(2, 10); // 6.0211363285087005

Rounds a number to a specified amount of digits.

Use Math.round() and template literals to round the number to the specified number of digits. Omit the second argument, decimals to round to an integer.

Code

const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);

Example

round(1.005, 2); // 1.01

Hashes the input string into a whole number.

Use String.prototype.split('') and Array.prototype.reduce() to create a hash of the input string, utilizing bit shifting.

Code

const sdbm = str => {
 let arr = str.split('');
 return arr.reduce(
   (hashCode, currentVal) =>
     (hashCode = currentVal.charCodeAt(0) + (hashCode << 6) + (hashCode << 16) - hashCode),
   0
 );
};

Example

sdbm('name'); // -3521204949

Returns the standard deviation of an array of numbers.

Use Array.prototype.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then determine the standard deviation. You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.

Code

const standardDeviation = (arr, usePopulation = false) => {
 const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
 return Math.sqrt(
   arr.reduce((acc, val) => acc.concat((val - mean) ** 2), []).reduce((acc, val) => acc + val, 0) /
     (arr.length - (usePopulation ? 0 : 1))
 );
};

Example

standardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample)
standardDeviation([10, 2, 38, 23, 38, 23, 21], true); // 12.29899614287479 (population)

Returns the sum of two or more numbers/arrays.

Use Array.prototype.reduce() to add each value to an accumulator, initialized with a value of 0.

Code

const sum = (...arr) => [...arr].reduce((acc, val) => acc + val, 0);

Example

sum(...[1, 2, 3, 4]); // 10

Returns the sum of an array, after mapping each element to a value using the provided function.

Use Array.prototype.map() to map each element to the value returned by fn, Array.prototype.reduce() to add each value to an accumulator, initialized with a value of 0.

Code

const sumBy = (arr, fn) =>
 arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0);

Example

sumBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 20
sumBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 20

Returns the sum of the powers of all the numbers from start to end (both inclusive).

Use Array.prototype.fill() to create an array of all the numbers in the target range, Array.prototype.map() and the exponent operator (**) to raise them to power and Array.prototype.reduce() to add them together. Omit the second argument, power, to use a default power of 2. Omit the third argument, start, to use a default starting value of 1.

Code

const sumPower = (end, power = 2, start = 1) =>
 Array(end + 1 - start)
   .fill(0)
   .map((x, i) => (i + start) ** power)
   .reduce((a, b) => a + b, 0);

Example

sumPower(10); // 385
sumPower(10, 3); //3025
sumPower(10, 3, 5); //2925

Converts a value to a safe integer.

Use Math.max() and Math.min() to find the closest safe value. Use Math.round() to convert to an integer.

Code

const toSafeInteger = num =>
 Math.round(Math.max(Math.min(num, Number.MAX_SAFE_INTEGER), Number.MIN_SAFE_INTEGER));

Example

toSafeInteger('3.2'); // 3
toSafeInteger(Infinity); // 9007199254740991

at res quokka.js:1664:0

Decodes a string of data which has been encoded using base-64 encoding.

Create a Buffer for the given string with base-64 encoding and use Buffer.toString('binary') to return the decoded string.

Code

const atob = str => new Buffer(str, 'base64').toString('binary');

Example

atob('Zm9vYmFy'); // 'foobar'

Creates a base-64 encoded ASCII string from a String object in which each character in the string is treated as a byte of binary data.

Create a Buffer for the given string with binary encoding and use Buffer.toString('base64') to return the encoded string.

Code

const btoa = str => new Buffer(str, 'binary').toString('base64');

Example

btoa('foobar'); // 'Zm9vYmFy'

Add special characters to text to print in color in the console (combined with console.log()).

Use template literals and special characters to add the appropriate color code to the string output. For background colors, add a special character that resets the background color at the end of the string.

Code

const colorize = (...args) => ({
 black: `\x1b[30m${args.join(' ')}`,
 red: `\x1b[31m${args.join(' ')}`,
 green: `\x1b[32m${args.join(' ')}`,
 yellow: `\x1b[33m${args.join(' ')}`,
 blue: `\x1b[34m${args.join(' ')}`,
 magenta: `\x1b[35m${args.join(' ')}`,
 cyan: `\x1b[36m${args.join(' ')}`,
 white: `\x1b[37m${args.join(' ')}`,
 bgBlack: `\x1b[40m${args.join(' ')}\x1b[0m`,
 bgRed: `\x1b[41m${args.join(' ')}\x1b[0m`,
 bgGreen: `\x1b[42m${args.join(' ')}\x1b[0m`,
 bgYellow: `\x1b[43m${args.join(' ')}\x1b[0m`,
 bgBlue: `\x1b[44m${args.join(' ')}\x1b[0m`,
 bgMagenta: `\x1b[45m${args.join(' ')}\x1b[0m`,
 bgCyan: `\x1b[46m${args.join(' ')}\x1b[0m`,
 bgWhite: `\x1b[47m${args.join(' ')}\x1b[0m`
});

Example

console.log(colorize('foo').red); // 'foo' (red letters)
console.log(colorize('foo', 'bar').bgBlue); // 'foo bar' (blue background)
console.log(colorize(colorize('foo').yellow, colorize('foo').green).bgWhite); // 'foo bar' (first word in yellow letters, second word in green letters, white background for both)

Check if the current process's arguments contain the specified flags.

Use Array.prototype.every() and Array.prototype.includes() to check if process.argv contains all the specified flags. Use a regular expression to test if the specified flags are prefixed with - or -- and prefix them accordingly.

Code

const hasFlags = (...flags) =>
 flags.every(flag => process.argv.includes(/^-{1,2}/.test(flag) ? flag : '--' + flag));

Example

// node myScript.js -s --test --cool=true
hasFlags('-s'); // true
hasFlags('--test', 'cool=true', '-s'); // true
hasFlags('special'); // false

Creates a hash for a value using the SHA-256 algorithm. Returns a promise.

Use crypto API to create a hash for the given value.

Code

const crypto = require('crypto');
const hashNode = val =>
 new Promise(resolve =>
   setTimeout(
     () =>
       resolve(
         crypto
           .createHash('sha256')
           .update(val)
           .digest('hex')
       ),
     0
   )
 );

Example

hashNode(JSON.stringify({ a: 'a', b: [1, 2, 3, 4], foo: { c: 'bar' } })).then(console.log); // '04aa106279f5977f59f9067fa9712afc4aedc6f5862a8defc34552d8c7206393'

Checks if the current environment is Travis CI.

Checks if the current environment has the TRAVIS and CI environment variables (reference).

Code

const isTravisCI = () => 'TRAVIS' in process.env && 'CI' in process.env;

Example

isTravisCI(); // true (if code is running on Travis CI)

Writes a JSON object to a file.

Use fs.writeFile(), template literals and JSON.stringify() to write a json object to a .json file.

Code

const fs = require('fs');
const JSONToFile = (obj, filename) =>
 fs.writeFile(`${filename}.json`, JSON.stringify(obj, null, 2));

Example

JSONToFile({ test: 'is passed' }, 'testJsonFile'); // writes the object to 'testJsonFile.json'

Returns an array of lines from the specified file.

Use readFileSync function in fs node package to create a Buffer from a file. convert buffer to string using toString(encoding) function. creating an array from contents of file by spliting file content line by line (each \n).

Code

const fs = require('fs');
const readFileLines = filename =>
 fs
   .readFileSync(filename)
   .toString('UTF8')
   .split('\n');

Example

/*
contents of test.txt :
 line1
 line2
 line3
 ___________________________
*/
let arr = readFileLines('test.txt');
console.log(arr); // ['line1', 'line2', 'line3']

Converts a tilde path to an absolute path.

Use String.prototype.replace() with a regular expression and OS.homedir() to replace the ~ in the start of the path with the home directory.

Code

const untildify = str => str.replace(/^~($|\/|\\)/, `${require('os').homedir()}$1`);

Example

untildify('~/node'); // '/Users/aUser/node'

Generates a UUID in Node.JS.

Use crypto API to generate a UUID, compliant with RFC4122 version 4.

Code

const crypto = require('crypto');
const UUIDGeneratorNode = () =>
 ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
   (c ^ (crypto.randomBytes(1)[0] & (15 >> (c / 4)))).toString(16)
 );

Example

UUIDGeneratorNode(); // '79c7c136-60ee-40a2-beb2-856f1feabefc'

at res quokka.js:1664:0

Binds methods of an object to the object itself, overwriting the existing method.

Use Array.prototype.forEach() to return a function that uses Function.prototype.apply() to apply the given context (obj) to fn for each function specified.

Code

const bindAll = (obj, ...fns) =>
 fns.forEach(
   fn => (
     (f = obj[fn]),
     (obj[fn] = function() {
       return f.apply(obj);
     })
   )
 );

Example

var view = {
 label: 'docs',
 click: function() {
   console.log('clicked ' + this.label);
 }
};
bindAll(view, 'click');
jQuery(element).on('click', view.click); // Logs 'clicked docs' when clicked.

Creates a deep clone of an object.

Use recursion. Use Object.assign() and an empty object ({}) to create a shallow clone of the original. Use Object.keys() and Array.prototype.forEach() to determine which key-value pairs need to be deep cloned.

Code

const deepClone = obj => {
 let clone = Object.assign({}, obj);
 Object.keys(clone).forEach(
   key => (clone[key] = typeof obj[key] === 'object' ? deepClone(obj[key]) : obj[key])
 );
 return Array.isArray(obj) ? (clone.length = obj.length) && Array.from(clone) : clone;
};

Example

const a = { foo: 'bar', obj: { a: 1, b: 2 } };
const b = deepClone(a); // a !== b, a.obj !== b.obj

Deep freezes an object.

Calls Object.freeze(obj) recursively on all unfrozen properties of passed object that are instanceof object.

Code

const deepFreeze = obj =>
 Object.keys(obj).forEach(
   prop =>
     !obj[prop] instanceof Object || Object.isFrozen(obj[prop]) ? null : deepFreeze(obj[prop])
 ) || Object.freeze(obj);

Example

'use strict';

const o = deepFreeze([1, [2, 3]]);

o[0] = 3; // not allowed
o[1][0] = 4; // not allowed as well

Assigns default values for all properties in an object that are undefined.

Use Object.assign() to create a new empty object and copy the original one to maintain key order, use Array.prototype.reverse() and the spread operator ... to combine the default values from left to right, finally use obj again to overwrite properties that originally had a value.

Code

const defaults = (obj, ...defs) => Object.assign({}, obj, ...defs.reverse(), obj);

Example

defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 }); // { a: 1, b: 2 }

Returns the target value in a nested JSON object, based on the given key.

Use the in operator to check if target exists in obj. If found, return the value of obj[target], otherwise use Object.values(obj) and Array.prototype.reduce() to recursively call dig on each nested object until the first matching key/value pair is found.

Code

const dig = (obj, target) =>
 target in obj
   ? obj[target]
   : Object.values(obj).reduce((acc, val) => {
       if (acc !== undefined) return acc;
       if (typeof val === 'object') return dig(val, target);
     }, undefined);

Example

const data = {
 level1: {
   level2: {
     level3: 'some data'
   }
 }
};
dig(data, 'level3'); // 'some data'
dig(data, 'level4'); // undefined

Performs a deep comparison between two values to determine if they are equivalent.

Check if the two values are identical, if they are both Date objects with the same time, using Date.getTime() or if they are both non-object values with an equivalent value (strict comparison). Check if only one value is null or undefined or if their prototypes differ. If none of the above conditions are met, use Object.keys() to check if both values have the same number of keys, then use Array.prototype.every() to check if every key in the first value exists in the second one and if they are equivalent by calling this method recursively.

Code

const equals = (a, b) => {
 if (a === b) return true;
 if (a instanceof Date && b instanceof Date) return a.getTime() === b.getTime();
 if (!a || !b || (typeof a !== 'object' && typeof b !== 'object')) return a === b;
 if (a === null || a === undefined || b === null || b === undefined) return false;
 if (a.prototype !== b.prototype) return false;
 let keys = Object.keys(a);
 if (keys.length !== Object.keys(b).length) return false;
 return keys.every(k => equals(a[k], b[k]));
};

Example

equals({ a: [2, { e: 3 }], b: [4], c: 'foo' }, { a: [2, { e: 3 }], b: [4], c: 'foo' }); // true

Returns the first key that satisfies the provided testing function. Otherwise undefined is returned.

Use Object.keys(obj) to get all the properties of the object, Array.prototype.find() to test the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.

Code

const findKey = (obj, fn) => Object.keys(obj).find(key => fn(obj[key], key, obj));

Example

findKey(
 {
   barney: { age: 36, active: true },
   fred: { age: 40, active: false },
   pebbles: { age: 1, active: true }
 },
 o => o['active']
); // 'barney'

Returns the last key that satisfies the provided testing function.

Otherwise undefined is returned.

Use Object.keys(obj) to get all the properties of the object, Array.prototype.reverse() to reverse their order and Array.prototype.find() to test the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.

Code

const findLastKey = (obj, fn) =>
 Object.keys(obj)
   .reverse()
   .find(key => fn(obj[key], key, obj));

Example

findLastKey(
 {
   barney: { age: 36, active: true },
   fred: { age: 40, active: false },
   pebbles: { age: 1, active: true }
 },
 o => o['active']
); // 'pebbles'

Flatten an object with the paths for keys.

Use recursion. Use Object.keys(obj) combined with Array.prototype.reduce() to convert every leaf node to a flattened path node. If the value of a key is an object, the function calls itself with the appropriate prefix to create the path using Object.assign(). Otherwise, it adds the appropriate prefixed key-value pair to the accumulator object. You should always omit the second argument, prefix, unless you want every key to have a prefix.

Code

const flattenObject = (obj, prefix = '') =>
 Object.keys(obj).reduce((acc, k) => {
   const pre = prefix.length ? prefix + '.' : '';
   if (typeof obj[k] === 'object') Object.assign(acc, flattenObject(obj[k], pre + k));
   else acc[pre + k] = obj[k];
   return acc;
 }, {});

Example

flattenObject({ a: { b: { c: 1 } }, d: 1 }); // { 'a.b.c': 1, d: 1 }

Iterates over all own properties of an object, running a callback for each one.

Use Object.keys(obj) to get all the properties of the object, Array.prototype.forEach() to run the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.

Code

const forOwn = (obj, fn) => Object.keys(obj).forEach(key => fn(obj[key], key, obj));

Example

forOwn({ foo: 'bar', a: 1 }, v => console.log(v)); // 'bar', 1

Iterates over all own properties of an object in reverse, running a callback for each one.

Use Object.keys(obj) to get all the properties of the object, Array.prototype.reverse() to reverse their order and Array.prototype.forEach() to run the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.

Code

const forOwnRight = (obj, fn) =>
 Object.keys(obj)
   .reverse()
   .forEach(key => fn(obj[key], key, obj));

Example

forOwnRight({ foo: 'bar', a: 1 }, v => console.log(v)); // 1, 'bar'

Returns an array of function property names from own (and optionally inherited) enumerable properties of an object.

Use Object.keys(obj) to iterate over the object's own properties. If inherited is true, use Object.get.PrototypeOf(obj) to also get the object's inherited properties. Use Array.prototype.filter() to keep only those properties that are functions. Omit the second argument, inherited, to not include inherited properties by default.

Code

const functions = (obj, inherited = false) =>
 (inherited
   ? [...Object.keys(obj), ...Object.keys(Object.getPrototypeOf(obj))]
   : Object.keys(obj)
 ).filter(key => typeof obj[key] === 'function');

Example

function Foo() {
 this.a = () => 1;
 this.b = () => 2;
}
Foo.prototype.c = () => 3;
functions(new Foo()); // ['a', 'b']
functions(new Foo(), true); // ['a', 'b', 'c']

Retrieve a set of properties indicated by the given selectors from an object.

Use Array.prototype.map() for each selector, String.prototype.replace() to replace square brackets with dots, String.prototype.split('.') to split each selector, Array.prototype.filter() to remove empty values and Array.prototype.reduce() to get the value indicated by it.

Code

const get = (from, ...selectors) =>
 [...selectors].map(s =>
   s
     .replace(/\[([^\[\]]*)\]/g, '.$1.')
     .split('.')
     .filter(t => t !== '')
     .reduce((prev, cur) => prev && prev[cur], from)
 );

Example

const obj = { selector: { to: { val: 'val to select' } }, target: [1, 2, { a: 'test' }] };
get(obj, 'selector.to.val', 'target[0]', 'target[2].a'); // ['val to select', 1, 'test']

Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.

Use Object.keys() and Array.prototype.reduce() to invert the key-value pairs of an object and apply the function provided (if any). Omit the second argument, fn, to get the inverted keys without applying a function to them.

Code

const invertKeyValues = (obj, fn) =>
 Object.keys(obj).reduce((acc, key) => {
   const val = fn ? fn(obj[key]) : obj[key];
   acc[val] = acc[val] || [];
   acc[val].push(key);
   return acc;
 }, {});

Example

invertKeyValues({ a: 1, b: 2, c: 1 }); // { 1: [ 'a', 'c' ], 2: [ 'b' ] }
invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value); // { group1: [ 'a', 'c' ], group2: [ 'b' ] }

Creates a new object from the specified object, where all the keys are in lowercase.

Use Object.keys() and Array.prototype.reduce() to create a new object from the specified object. Convert each key in the original object to lowercase, using String.toLowerCase().

Code

const lowercaseKeys = obj =>
 Object.keys(obj).reduce((acc, key) => {
   acc[key.toLowerCase()] = obj[key];
   return acc;
 }, {});

Example

const myObj = { Name: 'Adam', sUrnAME: 'Smith' };
const myObjLower = lowercaseKeys(myObj); // {name: 'Adam', surname: 'Smith'};

Creates an object with keys generated by running the provided function for each key and the same values as the provided object.

Use Object.keys(obj) to iterate over the object's keys. Use Array.prototype.reduce() to create a new object with the same values and mapped keys using fn.

Code

const mapKeys = (obj, fn) =>
 Object.keys(obj).reduce((acc, k) => {
   acc[fn(obj[k], k, obj)] = obj[k];
   return acc;
 }, {});

Example

mapKeys({ a: 1, b: 2 }, (val, key) => key + val); // { a1: 1, b2: 2 }

Creates an object with the same keys as the provided object and values generated by running the provided function for each value.

Use Object.keys(obj) to iterate over the object's keys. Use Array.prototype.reduce() to create a new object with the same keys and mapped values using fn.

Code

const mapValues = (obj, fn) =>
 Object.keys(obj).reduce((acc, k) => {
   acc[k] = fn(obj[k], k, obj);
   return acc;
 }, {});

Example

const users = {
 fred: { user: 'fred', age: 40 },
 pebbles: { user: 'pebbles', age: 1 }
};
mapValues(users, u => u.age); // { fred: 40, pebbles: 1 }

Compares two objects to determine if the first one contains equivalent property values to the second one.

Use Object.keys(source) to get all the keys of the second object, then Array.prototype.every(), Object.hasOwnProperty() and strict comparison to determine if all keys exist in the first object and have the same values.

Code

const matches = (obj, source) =>
 Object.keys(source).every(key => obj.hasOwnProperty(key) && obj[key] === source[key]);

Example

matches({ age: 25, hair: 'long', beard: true }, { hair: 'long', beard: true }); // true
matches({ hair: 'long', beard: true }, { age: 25, hair: 'long', beard: true }); // false

Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.

Use Object.keys(source) to get all the keys of the second object, then Array.prototype.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.

Code

const matchesWith = (obj, source, fn) =>
 Object.keys(source).every(
   key =>
     obj.hasOwnProperty(key) && fn
       ? fn(obj[key], source[key], key, obj, source)
       : obj[key] == source[key]
 );

Example

const isGreeting = val => /^h(?:i|ello)$/.test(val);
matchesWith(
 { greeting: 'hello' },
 { greeting: 'hi' },
 (oV, sV) => isGreeting(oV) && isGreeting(sV)
); // true

Creates a new object from the combination of two or more objects.

Use Array.prototype.reduce() combined with Object.keys(obj) to iterate over all objects and keys. Use hasOwnProperty() and Array.prototype.concat() to append values for keys existing in multiple objects.

Code

const merge = (...objs) =>
 [...objs].reduce(
   (acc, obj) =>
     Object.keys(obj).reduce((a, k) => {
       acc[k] = acc.hasOwnProperty(k) ? [].concat(acc[k]).concat(obj[k]) : obj[k];
       return acc;
     }, {}),
   {}
 );

Example

const object = {
 a: [{ x: 2 }, { y: 4 }],
 b: 1
};
const other = {
 a: { z: 3 },
 b: [2, 3],
 c: 'foo'
};
merge(object, other); // { a: [ { x: 2 }, { y: 4 }, { z: 3 } ], b: [ 1, 2, 3 ], c: 'foo' }

Given a flat array of objects linked to one another, it will nest them recursively.

Useful for nesting comments, such as the ones on reddit.com.

Use recursion. Use Array.prototype.filter() to filter the items where the id matches the link, then Array.prototype.map() to map each one to a new object that has a children property which recursively nests the items based on which ones are children of the current item. Omit the second argument, id, to default to null which indicates the object is not linked to another one (i.e. it is a top level object). Omit the third argument, link, to use 'parent_id' as the default property which links the object to another one by its id.

Code

const nest = (items, id = null, link = 'parent_id') =>
 items
   .filter(item => item[link] === id)
   .map(item => ({ ...item, children: nest(items, item.id) }));

Example

// One top level comment
const comments = [
 { id: 1, parent_id: null },
 { id: 2, parent_id: 1 },
 { id: 3, parent_id: 1 },
 { id: 4, parent_id: 2 },
 { id: 5, parent_id: 4 }
];
const nestedComments = nest(comments); // [{ id: 1, parent_id: null, children: [...] }]

Creates an object from the given key-value pairs.

Use Array.prototype.reduce() to create and combine key-value pairs.

Code

const objectFromPairs = arr => arr.reduce((a, [key, val]) => ((a[key] = val), a), {});

Example

objectFromPairs([['a', 1], ['b', 2]]); // {a: 1, b: 2}

Creates an array of key-value pair arrays from an object.

Use Object.keys() and Array.prototype.map() to iterate over the object's keys and produce an array with key-value pairs.

Code

const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);

Example

objectToPairs({ a: 1, b: 2 }); // [ ['a', 1], ['b', 2] ]

Omits the key-value pairs corresponding to the given keys from an object.

Use Object.keys(obj), Array.prototype.filter() and Array.prototype.includes() to remove the provided keys. Use Array.prototype.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.

Code

const omit = (obj, arr) =>
 Object.keys(obj)
   .filter(k => !arr.includes(k))
   .reduce((acc, key) => ((acc[key] = obj[key]), acc), {});

Example

omit({ a: 1, b: '2', c: 3 }, ['b']); // { 'a': 1, 'c': 3 }

Creates an object composed of the properties the given function returns falsey for. The function is invoked with two arguments: (value, key).

Use Object.keys(obj) and Array.prototype.filter()to remove the keys for which fn returns a truthy value. Use Array.prototype.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.

Code

const omitBy = (obj, fn) =>
 Object.keys(obj)
   .filter(k => !fn(obj[k], k))
   .reduce((acc, key) => ((acc[key] = obj[key]), acc), {});

Example

omitBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number'); // { b: '2' }

Returns a sorted array of objects ordered by properties and orders.

Uses Array.prototype.sort(), Array.prototype.reduce() on the props array with a default value of 0, use array destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.

Code

const orderBy = (arr, props, orders) =>
 [...arr].sort((a, b) =>
   props.reduce((acc, prop, i) => {
     if (acc === 0) {
       const [p1, p2] = orders && orders[i] === 'desc' ? [b[prop], a[prop]] : [a[prop], b[prop]];
       acc = p1 > p2 ? 1 : p1 < p2 ? -1 : 0;
     }
     return acc;
   }, 0)
 );

Example

const users = [{ name: 'fred', age: 48 }, { name: 'barney', age: 36 }, { name: 'fred', age: 40 }];
orderBy(users, ['name', 'age'], ['asc', 'desc']); // [{name: 'barney', age: 36}, {name: 'fred', age: 48}, {name: 'fred', age: 40}]
orderBy(users, ['name', 'age']); // [{name: 'barney', age: 36}, {name: 'fred', age: 40}, {name: 'fred', age: 48}]

Picks the key-value pairs corresponding to the given keys from an object.

Use Array.prototype.reduce() to convert the filtered/picked keys back to an object with the corresponding key-value pairs if the key exists in the object.

Code

const pick = (obj, arr) =>
 arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});

Example

pick({ a: 1, b: '2', c: 3 }, ['a', 'c']); // { 'a': 1, 'c': 3 }

Creates an object composed of the properties the given function returns truthy for. The function is invoked with two arguments: (value, key).

Use Object.keys(obj) and Array.prototype.filter()to remove the keys for which fn returns a falsey value. Use Array.prototype.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.

Code

const pickBy = (obj, fn) =>
 Object.keys(obj)
   .filter(k => fn(obj[k], k))
   .reduce((acc, key) => ((acc[key] = obj[key]), acc), {});

Example

pickBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number'); // { 'a': 1, 'c': 3 }

Replaces the names of multiple object keys with the values provided.

Use Object.keys() in combination with Array.prototype.reduce() and the spread operator (...) to get the object's keys and rename them according to keysMap.

Code

const renameKeys = (keysMap, obj) =>
 Object.keys(obj).reduce(
   (acc, key) => ({
     ...acc,
     ...{ [keysMap[key] || key]: obj[key] }
   }),
   {}
 );

Example

const obj = { name: 'Bobo', job: 'Front-End Master', shoeSize: 100 };
renameKeys({ name: 'firstName', job: 'passion' }, obj); // { firstName: 'Bobo', passion: 'Front-End Master', shoeSize: 100 }

Creates a shallow clone of an object.

Use Object.assign() and an empty object ({}) to create a shallow clone of the original.

Code

const shallowClone = obj => Object.assign({}, obj);

Example

const a = { x: true, y: 1 };
const b = shallowClone(a); // a !== b

Get size of arrays, objects or strings.

Get type of val (array, object or string). Use length property for arrays. Use length or size value if available or number of keys for objects. Use size of a Blob object created from val for strings.

Split strings into array of characters with split('') and return its length.

Code

const size = val =>
 Array.isArray(val)
   ? val.length
   : val && typeof val === 'object'
     ? val.size || val.length || Object.keys(val).length
     : typeof val === 'string'
       ? new Blob([val]).size
       : 0;

Example

size([1, 2, 3, 4, 5]); // 5
size('size'); // 4
size({ one: 1, two: 2, three: 3 }); // 3

Applies a function against an accumulator and each key in the object (from left to right).

Use Object.keys(obj) to iterate over each key in the object, Array.prototype.reduce() to call the apply the specified function against the given accumulator.

Code

const transform = (obj, fn, acc) => Object.keys(obj).reduce((a, k) => fn(a, obj[k], k, obj), acc);

Example

transform(
 { a: 1, b: 2, c: 1 },
 (r, v, k) => {
   (r[v] || (r[v] = [])).push(k);
   return r;
 },
 {}
); // { '1': ['a', 'c'], '2': ['b'] }

Checks if the predicate (second argument) is truthy on all elements of a collection (first argument).

Use Array.prototype.every() to check if each passed object has the specified property and if it returns a truthy value.

Code

const truthCheckCollection = (collection, pre) => collection.every(obj => obj[pre]);

Example

truthCheckCollection([{ user: 'Tinky-Winky', sex: 'male' }, { user: 'Dipsy', sex: 'male' }], 'sex'); // true

Unflatten an object with the paths for keys.

Use Object.keys(obj) combined with Array.prototype.reduce() to convert flattened path node to a leaf node. If the value of a key contains a dot delimiter (.), use Array.prototype.split('.'), string transformations and JSON.parse() to create an object, then Object.assign() to create the leaf node. Otherwise, add the appropriate key-value pair to the accumulator object.

Code

const unflattenObject = obj =>
 Object.keys(obj).reduce((acc, k) => {
   if (k.indexOf('.') !== -1) {
     const keys = k.split('.');
     Object.assign(
       acc,
       JSON.parse(
         '{' +
           keys.map((v, i) => (i !== keys.length - 1 ? `"${v}":{` : `"${v}":`)).join('') +
           obj[k] +
           '}'.repeat(keys.length)
       )
     );
   } else acc[k] = obj[k];
   return acc;
 }, {});

Example

unflattenObject({ 'a.b.c': 1, d: 1 }); // { a: { b: { c: 1 } }, d: 1 }

Returns the length of a string in bytes.

Convert a given string to a Blob Object and find its size.

Code

const byteSize = str => new Blob([str]).size;

Example

byteSize('😀'); // 4
byteSize('Hello World'); // 11

Capitalizes the first letter of a string.

Use array destructuring and String.prototype.toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.prototype.join('') to make it a string again. Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lowercase.

Code

const capitalize = ([first, ...rest], lowerRest = false) =>
 first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));

Example

capitalize('fooBar'); // 'FooBar'
capitalize('fooBar', true); // 'Foobar'

Capitalizes the first letter of every word in a string.

Use String.prototype.replace() to match the first character of each word and String.prototype.toUpperCase() to capitalize it.

Code

const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());

Example

capitalizeEveryWord('hello world!'); // 'Hello World!'

Converts a comma-separated values (CSV) string to a 2D array.

Use Array.prototype.slice() and Array.prototype.indexOf('\n') to remove the first row (title row) if omitFirstRow is true. Use String.prototype.split('\n') to create a string for each row, then String.prototype.split(delimiter) to separate the values in each row. Omit the second argument, delimiter, to use a default delimiter of ,. Omit the third argument, omitFirstRow, to include the first row (title row) of the CSV string.

Code

const CSVToArray = (data, delimiter = ',', omitFirstRow = false) =>
 data
   .slice(omitFirstRow ? data.indexOf('\n') + 1 : 0)
   .split('\n')
   .map(v => v.split(delimiter));

Example

CSVToArray('a,b\nc,d'); // [['a','b'],['c','d']];
CSVToArray('a;b\nc;d', ';'); // [['a','b'],['c','d']];
CSVToArray('col1,col2\na,b\nc,d', ',', true); // [['a','b'],['c','d']];

Converts a comma-separated values (CSV) string to a 2D array of objects.

The first row of the string is used as the title row.

Use Array.prototype.slice() and Array.prototype.indexOf('\n') and String.prototype.split(delimiter) to separate the first row (title row) into values. Use String.prototype.split('\n') to create a string for each row, then Array.prototype.map() and String.prototype.split(delimiter) to separate the values in each row. Use Array.prototype.reduce() to create an object for each row's values, with the keys parsed from the title row. Omit the second argument, delimiter, to use a default delimiter of ,.

Code

const CSVToJSON = (data, delimiter = ',') => {
 const titles = data.slice(0, data.indexOf('\n')).split(delimiter);
 return data
   .slice(data.indexOf('\n') + 1)
   .split('\n')
   .map(v => {
     const values = v.split(delimiter);
     return titles.reduce((obj, title, index) => ((obj[title] = values[index]), obj), {});
   });
};

Example

CSVToJSON('col1,col2\na,b\nc,d'); // [{'col1': 'a', 'col2': 'b'}, {'col1': 'c', 'col2': 'd'}];
CSVToJSON('col1;col2\na;b\nc;d', ';'); // [{'col1': 'a', 'col2': 'b'}, {'col1': 'c', 'col2': 'd'}];

Decapitalizes the first letter of a string.

Use array destructuring and String.toLowerCase() to decapitalize first letter, ...rest to get array of characters after first letter and then Array.prototype.join('') to make it a string again. Omit the upperRest parameter to keep the rest of the string intact, or set it to true to convert to uppercase.

Code

const decapitalize = ([first, ...rest], upperRest = false) =>
 first.toLowerCase() + (upperRest ? rest.join('').toUpperCase() : rest.join(''));

Example

decapitalize('FooBar'); // 'fooBar'
decapitalize('FooBar', true); // 'fOOBAR'

Escapes a string for use in HTML.

Use String.prototype.replace() with a regexp that matches the characters that need to be escaped, using a callback function to replace each character instance with its associated escaped character using a dictionary (object).

Code

const escapeHTML = str =>
 str.replace(
   /[&<>'"]/g,
   tag =>
     ({
       '&': '&amp;',
       '<': '&lt;',
       '>': '&gt;',
       "'": '&#39;',
       '"': '&quot;'
     }[tag] || tag)
 );

Example

escapeHTML('<a href="#">Me & you</a>'); // '&lt;a href=&quot;#&quot;&gt;Me &amp; you&lt;/a&gt;'

Escapes a string to use in a regular expression.

Use String.prototype.replace() to escape special characters.

Code

const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');

Example

escapeRegExp('(test)'); // \\(test\\)

Converts a string from camelcase.

Use String.prototype.replace() to remove underscores, hyphens, and spaces and convert words to camelcase. Omit the second argument to use a default separator of _.

Code

const fromCamelCase = (str, separator = '_') =>
 str
   .replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
   .replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2')
   .toLowerCase();

Example

fromCamelCase('someDatabaseFieldName', ' '); // 'some database field name'
fromCamelCase('someLabelThatNeedsToBeCamelized', '-'); // 'some-label-that-needs-to-be-camelized'
fromCamelCase('someJavascriptProperty', '_'); // 'some_javascript_property'

Indents each line in the provided string.

Use String.replace and a regular expression to add the character specified by indent count times at the start of each line. Omit the third parameter, indent, to use a default indentation character of ' '.

Code

const indentString = (str, count, indent = ' ') => str.replace(/^/gm, indent.repeat(count));

Example

indentString('Lorem\nIpsum', 2); // '  Lorem\n  Ipsum'
indentString('Lorem\nIpsum', 2, '_'); // '__Lorem\n__Ipsum'

Returns true if the given string is an absolute URL, false otherwise.

Use a regular expression to test if the string is an absolute URL.

Code

const isAbsoluteURL = str => /^[a-z][a-z0-9+.-]*:/.test(str);

Example

isAbsoluteURL('https://google.com'); // true
isAbsoluteURL('ftp://www.myserver.net'); // true
isAbsoluteURL('/foo/bar'); // false

Checks if a string is an anagram of another string (case-insensitive, ignores spaces, punctuation and special characters).

Use String.toLowerCase(), String.prototype.replace() with an appropriate regular expression to remove unnecessary characters, String.prototype.split(''), Array.prototype.sort() and Array.prototype.join('') on both strings to normalize them, then check if their normalized forms are equal.

Code

const isAnagram = (str1, str2) => {
 const normalize = str =>
   str
     .toLowerCase()
     .replace(/[^a-z0-9]/gi, '')
     .split('')
     .sort()
     .join('');
 return normalize(str1) === normalize(str2);
};

Example

isAnagram('iceman', 'cinema'); // true

Checks if a string is lower case.

Convert the given string to lower case, using String.toLowerCase() and compare it to the original.

Code

const isLowerCase = str => str === str.toLowerCase();

Example

isLowerCase('abc'); // true
isLowerCase('a3@$'); // true
isLowerCase('Ab4'); // false

Checks if a string is upper case.

Convert the given string to upper case, using String.prototype.toUpperCase() and compare it to the original.

Code

const isUpperCase = str => str === str.toUpperCase();

Example

isUpperCase('ABC'); // true
isLowerCase('A3@$'); // true
isLowerCase('aB4'); // false

Creates a new string with the results of calling a provided function on every character in the calling string.

Use String.prototype.split('') and Array.prototype.map() to call the provided function, fn, for each character in str. Use Array.prototype.join('') to recombine the array of characters into a string. The callback function, fn, takes three arguments (the current character, the index of the current character and the string mapString was called upon).

Code

const mapString = (str, fn) =>
 str
   .split('')
   .map((c, i) => fn(c, i, str))
   .join('');

Example

mapString('lorem ipsum', c => c.toUpperCase()); // 'LOREM IPSUM'

Replaces all but the last num of characters with the specified mask character.

Use String.prototype.slice() to grab the portion of the characters that will remain unmasked and use String.padStart() to fill the beginning of the string with the mask character up to the original length. Omit the second argument, num, to keep a default of 4 characters unmasked. If num is negative, the unmasked characters will be at the start of the string. Omit the third argument, mask, to use a default character of '*' for the mask.

Code

const mask = (cc, num = 4, mask = '*') => `${cc}`.slice(-num).padStart(`${cc}`.length, mask);

Example

mask(1234567890); // '******7890'
mask(1234567890, 3); // '*******890'
mask(1234567890, -4, '$'); // '$$$$567890'

Pads a string on both sides with the specified character, if it's shorter than the specified length.

Use String.padStart() and String.padEnd() to pad both sides of the given string. Omit the third argument, char, to use the whitespace character as the default padding character.

Code

const pad = (str, length, char = ' ') =>
 str.padStart((str.length + length) / 2, char).padEnd(length, char);

Example

pad('cat', 8); // '  cat   '
pad(String(42), 6, '0'); // '004200'
pad('foobar', 3); // 'foobar'

Returns true if the given string is a palindrome, false otherwise.

Convert string String.toLowerCase() and use String.prototype.replace() to remove non-alphanumeric characters from it. Then, use the spread operator (...) to split string into individual characters, Array.prototype.reverse(), String.prototype.join('') and compare to the original, unreversed string, after converting it String.tolowerCase().

Code

const palindrome = str => {
 const s = str.toLowerCase().replace(/[\W_]/g, '');
 return s === [...s].reverse().join('');
};

Example

palindrome('taco cat'); // true

Returns the singular or plural form of the word based on the input number. If the first argument is an object, it will use a closure by returning a function that can auto-pluralize words that don't simply end in s if the supplied dictionary contains the word.

If num is either -1 or 1, return the singular form of the word. If num is any other number, return the plural form. Omit the third argument to use the default of the singular word + s, or supply a custom pluralized word when necessary. If the first argument is an object, utilize a closure by returning a function which can use the supplied dictionary to resolve the correct plural form of the word.

Code

const pluralize = (val, word, plural = word + 's') => {
 const _pluralize = (num, word, plural = word + 's') =>
   [1, -1].includes(Number(num)) ? word : plural;
 if (typeof val === 'object') return (num, word) => _pluralize(num, word, val[word]);
 return _pluralize(val, word, plural);
};

Example

pluralize(0, 'apple'); // 'apples'
pluralize(1, 'apple'); // 'apple'
pluralize(2, 'apple'); // 'apples'
pluralize(2, 'person', 'people'); // 'people'

const PLURALS = {
 person: 'people',
 radius: 'radii'
};
const autoPluralize = pluralize(PLURALS);
autoPluralize(2, 'person'); // 'people'

Removes non-printable ASCII characters.

Use a regular expression to remove non-printable ASCII characters.

Code

const removeNonASCII = str => str.replace(/[^\x20-\x7E]/g, '');

Example

removeNonASCII('äÄçÇéÉêlorem-ipsumöÖÐþúÚ'); // 'lorem-ipsum'

Reverses a string.

Use the spread operator (...) and Array.prototype.reverse() to reverse the order of the characters in the string. Combine characters to get a string using String.prototype.join('').

Code

const reverseString = str => [...str].reverse().join('');

Example

reverseString('foobar'); // 'raboof'

Alphabetically sorts the characters in a string.

Use the spread operator (...), Array.prototype.sort() and String.localeCompare() to sort the characters in str, recombine using String.prototype.join('').

Code

const sortCharactersInString = str => [...str].sort((a, b) => a.localeCompare(b)).join('');

Example

sortCharactersInString('cabbage'); // 'aabbceg'

Splits a multiline string into an array of lines.

Use String.prototype.split() and a regular expression to match line breaks and create an array.

Code

const splitLines = str => str.split(/\r?\n/);

Example

splitLines('This\nis a\nmultiline\nstring.\n'); // ['This', 'is a', 'multiline', 'string.' , '']

⚠️ WARNING: This function's execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your browser to hang as it tries to solve all the different combinations.

Generates all permutations of a string (contains duplicates).

Use recursion. For each letter in the given string, create all the partial permutations for the rest of its letters. Use Array.prototype.map() to combine the letter with each partial permutation, then Array.prototype.reduce() to combine all permutations in one array. Base cases are for string length equal to 2 or 1.

Code

const stringPermutations = str => {
 if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
 return str
   .split('')
   .reduce(
     (acc, letter, i) =>
       acc.concat(stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)),
     []
   );
};

Example

stringPermutations('abc'); // ['abc','acb','bac','bca','cab','cba']

Removes HTML/XML tags from string.

Use a regular expression to remove HTML/XML tags from a string.

Code

const stripHTMLTags = str => str.replace(/<[^>]*>/g, '');

Example

stripHTMLTags('<p><em>lorem</em> <strong>ipsum</strong></p>'); // 'lorem ipsum'

Converts a string to camelcase.

Break the string into words and combine them capitalizing the first letter of each word, using a regexp.

Code

const toCamelCase = str => {
 let s =
   str &&
   str
     .match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
     .map(x => x.slice(0, 1).toUpperCase() + x.slice(1).toLowerCase())
     .join('');
 return s.slice(0, 1).toLowerCase() + s.slice(1);
};

Example

toCamelCase('some_database_field_name'); // 'someDatabaseFieldName'
toCamelCase('Some label that needs to be camelized'); // 'someLabelThatNeedsToBeCamelized'
toCamelCase('some-javascript-property'); // 'someJavascriptProperty'
toCamelCase('some-mixed_string with spaces_underscores-and-hyphens'); // 'someMixedStringWithSpacesUnderscoresAndHyphens'

Converts a string to kebab case.

Break the string into words and combine them adding - as a separator, using a regexp.

Code

const toKebabCase = str =>
 str &&
 str
   .match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
   .map(x => x.toLowerCase())
   .join('-');

Example

toKebabCase('camelCase'); // 'camel-case'
toKebabCase('some text'); // 'some-text'
toKebabCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some-mixed-string-with-spaces-underscores-and-hyphens'
toKebabCase('AllThe-small Things'); // "all-the-small-things"
toKebabCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i-am-listening-to-fm-while-loading-different-url-on-my-browser-and-also-editing-xml-and-html"

Converts a string to snake case.

Break the string into words and combine them adding _ as a separator, using a regexp.

Code

const toSnakeCase = str =>
 str &&
 str
   .match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
   .map(x => x.toLowerCase())
   .join('_');

Example

toSnakeCase('camelCase'); // 'camel_case'
toSnakeCase('some text'); // 'some_text'
toSnakeCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some_mixed_string_with_spaces_underscores_and_hyphens'
toSnakeCase('AllThe-small Things'); // "all_the_smal_things"
toSnakeCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i_am_listening_to_fm_while_loading_different_url_on_my_browser_and_also_editing_some_xml_and_html"

Truncates a string up to a specified length.

Determine if the string's length is greater than num. Return the string truncated to the desired length, with '...' appended to the end or the original string.

Code

const truncateString = (str, num) =>
 str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;

Example

truncateString('boomerang', 7); // 'boom...'

Unescapes escaped HTML characters.

Use String.prototype.replace() with a regex that matches the characters that need to be unescaped, using a callback function to replace each escaped character instance with its associated unescaped character using a dictionary (object).

Code

const unescapeHTML = str =>
 str.replace(
   /&|<|>|'|"/g,
   tag =>
     ({
       '&': '&',
       '&lt;': '<',
       '&gt;': '>',
       '&#39;': "'",
       '&quot;': '"'
     }[tag] || tag)
 );

Example

unescapeHTML('&lt;a href=&quot;#&quot;&gt;Me &amp; you&lt;/a&gt;'); // '<a href="#">Me & you</a>'

Joins all given URL segments together, then normalizes the resulting URL.

Use String.prototype.join('/') to combine URL segments, then a series of String.prototype.replace() calls with various regexps to normalize the resulting URL (remove double slashes, add proper slashes for protocol, remove slashes before parameters, combine parameters with '&' and normalize first parameter delimiter).

Code

const URLJoin = (...args) =>
 args
   .join('/')
   .replace(/[\/]+/g, '/')
   .replace(/^(.+):\//, '$1://')
   .replace(/^file:/, 'file:/')
   .replace(/\/(\?|&|#[^!])/g, '$1')
   .replace(/\?/g, '&')
   .replace('&', '?');

Example

URLJoin('http://www.google.com', 'a', '/b/cd', '?foo=123', '?bar=foo'); // 'http://www.google.com/a/b/cd?foo=123&bar=foo'

Converts a given string into an array of words.

Use String.prototype.split() with a supplied pattern (defaults to non-alpha as a regexp) to convert to an array of strings. Use Array.prototype.filter() to remove any empty strings. Omit the second argument to use the default regexp.

Code

const words = (str, pattern = /[^a-zA-Z-]+/) => str.split(pattern).filter(Boolean);

Example

words('I love javaScript!!'); // ["I", "love", "javaScript"]
words('python, javaScript & coffee'); // ["python", "javaScript", "coffee"]

at res quokka.js:1664:0

Returns the native type of a value.

Returns lowercased constructor name of value, "undefined" or "null" if value is undefined or null.

Code

const getType = v =>
 v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();

Example

getType(new Set([1, 2, 3])); // 'set'

Checks if the provided value is of the specified type.

Ensure the value is not undefined or null using Array.prototype.includes(), and compare the constructor property on the value with type to check if the provided value is of the specified type.

Code

const is = (type, val) => ![, null].includes(val) && val.constructor === type;

Example

is(Array, [1]); // true
is(ArrayBuffer, new ArrayBuffer()); // true
is(Map, new Map()); // true
is(RegExp, /./g); // true
is(Set, new Set()); // true
is(WeakMap, new WeakMap()); // true
is(WeakSet, new WeakSet()); // true
is(String, ''); // true
is(String, new String('')); // true
is(Number, 1); // true
is(Number, new Number(1)); // true
is(Boolean, true); // true
is(Boolean, new Boolean(true)); // true

Checks if the provided argument is array-like (i.e. is iterable).

Check if the provided argument is not null and that its Symbol.iterator property is a function.

Code

const isArrayLike = obj => obj != null && typeof obj[Symbol.iterator] === 'function';

Example

isArrayLike(document.querySelectorAll('.className')); // true
isArrayLike('abc'); // true
isArrayLike(null); // false

Checks if the given argument is a native boolean element.

Use typeof to check if a value is classified as a boolean primitive.

Code

const isBoolean = val => typeof val === 'boolean';

Example

isBoolean(null); // false
isBoolean(false); // true

Returns true if the a value is an empty object, collection, map or set, has no enumerable properties or is any type that is not considered a collection.

Check if the provided value is null or if its length is equal to 0.

Code

const isEmpty = val => val == null || !(Object.keys(val) || val).length;

Example

isEmpty(new Map()); // true
isEmpty(new Set()); // true
isEmpty([]); // true
isEmpty({}); // true
isEmpty(''); // true
isEmpty([1, 2]); // false
isEmpty({ a: 1, b: 2 }); // false
isEmpty('text'); // false
isEmpty(123); // true - type is not considered a collection
isEmpty(true); // true - type is not considered a collection

Checks if the given argument is a function.

Use typeof to check if a value is classified as a function primitive.

Code

const isFunction = val => typeof val === 'function';

Example

isFunction('x'); // false
isFunction(x => x); // true

Returns true if the specified value is null or undefined, false otherwise.

Use the strict equality operator to check if the value and of val are equal to null or undefined.

Code

const isNil = val => val === undefined || val === null;

Example

isNil(null); // true
isNil(undefined); // true

Returns true if the specified value is null, false otherwise.

Use the strict equality operator to check if the value and of val are equal to null.

Code

const isNull = val => val === null;

Example

isNull(null); // true

Checks if the given argument is a number.

Use typeof to check if a value is classified as a number primitive.

Code

const isNumber = val => typeof val === 'number';

Example

isNumber('1'); // false
isNumber(1); // true

Returns a boolean determining if the passed value is an object or not.

Uses the Object constructor to create an object wrapper for the given value. If the value is null or undefined, create and return an empty object. Οtherwise, return an object of a type that corresponds to the given value.

Code

const isObject = obj => obj === Object(obj);

Example

isObject([1, 2, 3, 4]); // true
isObject([]); // true
isObject(['Hello!']); // true
isObject({ a: 1 }); // true
isObject({}); // true
isObject(true); // false

Checks if a value is object-like.

Check if the provided value is not null and its typeof is equal to 'object'.

Code

const isObjectLike = val => val !== null && typeof val === 'object';

Example

isObjectLike({}); // true
isObjectLike([1, 2, 3]); // true
isObjectLike(x => x); // false
isObjectLike(null); // false

Checks if the provided value is an object created by the Object constructor.

Check if the provided value is truthy, use typeof to check if it is an object and Object.constructor to make sure the constructor is equal to Object.

Code

const isPlainObject = val => !!val && typeof val === 'object' && val.constructor === Object;

Example

isPlainObject({ a: 1 }); // true
isPlainObject(new Map()); // false

Returns a boolean determining if the passed value is primitive or not.

Use Array.prototype.includes() on an array of type strings which are not primitive, supplying the type using typeof. Since typeof null evaluates to 'object', it needs to be directly compared.

Code

const isPrimitive = val => !['object', 'function'].includes(typeof val) || val === null;

Example

isPrimitive(null); // true
isPrimitive(50); // true
isPrimitive('Hello!'); // true
isPrimitive(false); // true
isPrimitive(Symbol()); // true
isPrimitive([]); // false

Returns true if an object looks like a Promise, false otherwise.

Check if the object is not null, its typeof matches either object or function and if it has a .then property, which is also a function.

Code

const isPromiseLike = obj =>
 obj !== null &&
 (typeof obj === 'object' || typeof obj === 'function') &&
 typeof obj.then === 'function';

Example

isPromiseLike({
 then: function() {
   return '';
 }
}); // true
isPromiseLike(null); // false
isPromiseLike({}); // false

Checks if the given argument is a string. Only works for string primitives.

Use typeof to check if a value is classified as a string primitive.

Code

const isString = val => typeof val === 'string';

Example

isString('10'); // true

Checks if the given argument is a symbol.

Use typeof to check if a value is classified as a symbol primitive.

Code

const isSymbol = val => typeof val === 'symbol';

Example

isSymbol(Symbol('x')); // true

Returns true if the specified value is undefined, false otherwise.

Use the strict equality operator to check if the value and of val are equal to undefined.

Code

const isUndefined = val => val === undefined;

Example

isUndefined(undefined); // true

Checks if the provided argument is a valid JSON.

Use JSON.parse() and a try... catch block to check if the provided argument is a valid JSON.

Code

const isValidJSON = obj => {
 try {
   JSON.parse(obj);
   return true;
 } catch (e) {
   return false;
 }
};

Example

isValidJSON('{"name":"Adam","age":20}'); // true
isValidJSON('{"name":"Adam",age:"20"}'); // false
isValidJSON(null); // true

at res quokka.js:1664:0

Casts the provided value as an array if it's not one.

Use Array.prototype.isArray() to determine if val is an array and return it as-is or encapsulated in an array accordingly.

Code

const castArray = val => (Array.isArray(val) ? val : [val]);

Example

castArray('foo'); // ['foo']
castArray([1]); // [1]

Clones a regular expression.

Use new RegExp(), RegExp.source and RegExp.flags to clone the given regular expression.

Code

const cloneRegExp = regExp => new RegExp(regExp.source, regExp.flags);

Example

const regExp = /lorem ipsum/gi;
const regExp2 = cloneRegExp(regExp); // /lorem ipsum/gi

Returns the first non-null/undefined argument.

Use Array.prototype.find() to return the first non null/undefined argument.

Code

const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_));

Example

coalesce(null, undefined, '', NaN, 'Waldo'); // ""

Returns a customized coalesce function that returns the first argument that returns true from the provided argument validation function.

Use Array.prototype.find() to return the first argument that returns true from the provided argument validation function.

Code

const coalesceFactory = valid => (...args) => args.find(valid);

Example

const customCoalesce = coalesceFactory(_ => ![null, undefined, '', NaN].includes(_));
customCoalesce(undefined, null, NaN, '', 'Waldo'); // "Waldo"

Extends a 3-digit color code to a 6-digit color code.

Use Array.prototype.map(), String.prototype.split() and Array.prototype.join() to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form. Array.prototype.slice() is used to remove # from string start since it's added once.

Code

const extendHex = shortHex =>
 '#' +
 shortHex
   .slice(shortHex.startsWith('#') ? 1 : 0)
   .split('')
   .map(x => x + x)
   .join('');

Example

extendHex('#03f'); // '#0033ff'
extendHex('05a'); // '#0055aa'

Returns an object containing the parameters of the current URL.

Use String.match() with an appropriate regular expression to get all key-value pairs, Array.prototype.reduce() to map and combine them into a single object. Pass location.search as the argument to apply to the current url.

Code

const getURLParameters = url =>
 (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
   (a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a),
   {}
 );

Example

getURLParameters('http://url.com/page?name=Adam&surname=Smith'); // {name: 'Adam', surname: 'Smith'}
getURLParameters('google.com'); // {}

Converts a color code to a rgb() or rgba() string if alpha value is provided.

Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.

Code

const hexToRGB = hex => {
 let alpha = false,
   h = hex.slice(hex.startsWith('#') ? 1 : 0);
 if (h.length === 3) h = [...h].map(x => x + x).join('');
 else if (h.length === 8) alpha = true;
 h = parseInt(h, 16);
 return (
   'rgb' +
   (alpha ? 'a' : '') +
   '(' +
   (h >>> (alpha ? 24 : 16)) +
   ', ' +
   ((h & (alpha ? 0x00ff0000 : 0x00ff00)) >>> (alpha ? 16 : 8)) +
   ', ' +
   ((h & (alpha ? 0x0000ff00 : 0x0000ff)) >>> (alpha ? 8 : 0)) +
   (alpha ? `, ${h & 0x000000ff}` : '') +
   ')'
 );
};

Example

hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)'
hexToRGB('27ae60'); // 'rgb(39, 174, 96)'
hexToRGB('#fff'); // 'rgb(255, 255, 255)'

Makes a GET request to the passed URL.

Use XMLHttpRequest web api to make a get request to the given url. Handle the onload event, by calling the given callback the responseText. Handle the onerror event, by running the provided err function. Omit the third argument, err, to log errors to the console's error stream by default.

Code

const httpGet = (url, callback, err = console.error) => {
 const request = new XMLHttpRequest();
 request.open('GET', url, true);
 request.onload = () => callback(request.responseText);
 request.onerror = () => err(request);
 request.send();
};

Example

httpGet(
 'https://jsonplaceholder.typicode.com/posts/1',
 console.log
); /* 
Logs: {
 "userId": 1,
 "id": 1,
 "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
 "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
}
*/

Makes a POST request to the passed URL.

Use XMLHttpRequest web api to make a post request to the given url. Set the value of an HTTP request header with setRequestHeader method. Handle the onload event, by calling the given callback the responseText. Handle the onerror event, by running the provided err function. Omit the third argument, data, to send no data to the provided url. Omit the fourth argument, err, to log errors to the console's error stream by default.

Code

const httpPost = (url, data, callback, err = console.error) => {
 const request = new XMLHttpRequest();
 request.open('POST', url, true);
 request.setRequestHeader('Content-type', 'application/json; charset=utf-8');
 request.onload = () => callback(request.responseText);
 request.onerror = () => err(request);
 request.send(data);
};

Example

const newPost = {
 userId: 1,
 id: 1337,
 title: 'Foo',
 body: 'bar bar bar'
};
const data = JSON.stringify(newPost);
httpPost(
 'https://jsonplaceholder.typicode.com/posts',
 data,
 console.log
); /*
Logs: {
 "userId": 1,
 "id": 1337,
 "title": "Foo",
 "body": "bar bar bar"
}
*/
httpPost(
 'https://jsonplaceholder.typicode.com/posts',
 null, //does not send a body
 console.log
); /*
Logs: {
 "id": 101
}
*/

Determines if the current runtime environment is a browser so that front-end modules can run on the server (Node) without throwing errors.

Use Array.prototype.includes() on the typeof values of both window and document (globals usually only available in a browser environment unless they were explicitly defined), which will return true if one of them is undefined. typeof allows globals to be checked for existence without throwing a ReferenceError. If both of them are not undefined, then the current environment is assumed to be a browser.

Code

const isBrowser = () => ![typeof window, typeof document].includes('undefined');

Example

isBrowser(); // true (browser)
isBrowser(); // false (Node)

Returns the index of the function in an array of functions which executed the fastest.

Use Array.prototype.map() to generate an array where each value is the total time taken to execute the function after iterations times. Use the difference in performance.now() values before and after to get the total time in milliseconds to a high degree of accuracy. Use Math.min() to find the minimum execution time, and return the index of that shortest time which corresponds to the index of the most performant function. Omit the second argument, iterations, to use a default of 10,000 iterations. The more iterations, the more reliable the result but the longer it will take.

Code

const mostPerformant = (fns, iterations = 10000) => {
 const times = fns.map(fn => {
   const before = performance.now();
   for (let i = 0; i < iterations; i++) fn();
   return performance.now() - before;
 });
 return times.indexOf(Math.min(...times));
};

Example

mostPerformant([
 () => {
   // Loops through the entire array before returning `false`
   [1, 2, 3, 4, 5, 6, 7, 8, 9, '10'].every(el => typeof el === 'number');
 },
 () => {
   // Only needs to reach index `1` before returning false
   [1, '2', 3, 4, 5, 6, 7, 8, 9, 10].every(el => typeof el === 'number');
 }
]); // 1

Creates a function that gets the argument at index n. If n is negative, the nth argument from the end is returned.

Use Array.prototype.slice() to get the desired argument at index n.

Code

const nthArg = n => (...args) => args.slice(n)[0];

Example

const third = nthArg(2);
third(1, 2, 3); // 3
third(1, 2); // undefined
const last = nthArg(-1);
last(1, 2, 3, 4, 5); // 5

Parse an HTTP Cookie header string and return an object of all cookie name-value pairs.

Use String.prototype.split(';') to separate key-value pairs from each other. Use Array.prototype.map() and String.prototype.split('=') to separate keys from values in each pair. Use Array.prototype.reduce() and decodeURIComponent() to create an object with all key-value pairs.

Code

const parseCookie = str =>
 str
   .split(';')
   .map(v => v.split('='))
   .reduce((acc, v) => {
     acc[decodeURIComponent(v[0].trim())] = decodeURIComponent(v[1].trim());
     return acc;
   }, {});

Example

parseCookie('foo=bar; equation=E%3Dmc%5E2'); // { foo: 'bar', equation: 'E=mc^2' }

Converts a number in bytes to a human-readable string.

Use an array dictionary of units to be accessed based on the exponent. Use Number.toPrecision() to truncate the number to a certain number of digits. Return the prettified string by building it up, taking into account the supplied options and whether it is negative or not. Omit the second argument, precision, to use a default precision of 3 digits. Omit the third argument, addSpace, to add space between the number and unit by default.

Code

const prettyBytes = (num, precision = 3, addSpace = true) => {
 const UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
 if (Math.abs(num) < 1) return num + (addSpace ? ' ' : '') + UNITS[0];
 const exponent = Math.min(Math.floor(Math.log10(num < 0 ? -num : num) / 3), UNITS.length - 1);
 const n = Number(((num < 0 ? -num : num) / 1000 ** exponent).toPrecision(precision));
 return (num < 0 ? '-' : '') + n + (addSpace ? ' ' : '') + UNITS[exponent];
};

Example

prettyBytes(1000); // "1 KB"
prettyBytes(-27145424323.5821, 5); // "-27.145 GB"
prettyBytes(123456789, 3, false); // "123MB"

Generates a random hexadecimal color code.

Use Math.random to generate a random 24-bit(6x4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal String using toString(16).

Code

const randomHexColorCode = () => {
 let n = (Math.random() * 0xfffff * 1000000).toString(16);
 return '#' + n.slice(0, 6);
};

Example

randomHexColorCode(); // "#e34155"

Converts the values of RGB components to a color code.

Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (<<) and toString(16), then String.padStart(6,'0') to get a 6-digit hexadecimal value.

Code

const RGBToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');

Example

RGBToHex(255, 165, 1); // 'ffa501'

Serialize a cookie name-value pair into a Set-Cookie header string.

Use template literals and encodeURIComponent() to create the appropriate string.

Code

const serializeCookie = (name, val) => `${encodeURIComponent(name)}=${encodeURIComponent(val)}`;

Example

serializeCookie('foo', 'bar'); // 'foo=bar'

Measures the time taken by a function to execute.

Use console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.

Code

const timeTaken = callback => {
 console.time('timeTaken');
 const r = callback();
 console.timeEnd('timeTaken');
 return r;
};

Example

timeTaken(() => Math.pow(2, 10)); // 1024, (logged): timeTaken: 0.02099609375ms

Take a number and return specified currency formatting.

Use Intl.NumberFormat to enable country / currency sensitive formatting.

Code

const toCurrency = (n, curr, LanguageFormat = undefined) =>
 Intl.NumberFormat(LanguageFormat, { style: 'currency', currency: curr }).format(n);

Example

toCurrency(123456.789, 'EUR'); // €123,456.79  | currency: Euro | currencyLangFormat: Local
toCurrency(123456.789, 'USD', 'en-us'); // $123,456.79  | currency: US Dollar | currencyLangFormat: English (United States)
toCurrency(123456.789, 'USD', 'fa'); // ۱۲۳٬۴۵۶٫۷۹ ؜$ | currency: US Dollar | currencyLangFormat: Farsi
toCurrency(322342436423.2435, 'JPY'); // ¥322,342,436,423 | currency: Japanese Yen | currencyLangFormat: Local
toCurrency(322342436423.2435, 'JPY', 'fi'); // 322 342 436 423 ¥ | currency: Japanese Yen | currencyLangFormat: Finnish

Use toLocaleString() to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.

Code

const toDecimalMark = num => num.toLocaleString('en-US');

Example

toDecimalMark(12305030388.9087); // "12,305,030,388.909"

Adds an ordinal suffix to a number.

Use the modulo operator (%) to find values of single and tens digits. Find which ordinal pattern digits match. If digit is found in teens pattern, use teens ordinal.

Code

const toOrdinalSuffix = num => {
 const int = parseInt(num),
   digits = [int % 10, int % 100],
   ordinals = ['st', 'nd', 'rd', 'th'],
   oPattern = [1, 2, 3, 4],
   tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
 return oPattern.includes(digits[0]) && !tPattern.includes(digits[1])
   ? int + ordinals[digits[0] - 1]
   : int + ordinals[3];
};

Example

toOrdinalSuffix('123'); // "123rd"

Returns true if the given value is a number, false otherwise.

Use !isNaN() in combination with parseFloat() to check if the argument is a number. Use isFinite() to check if the number is finite. Use Number() to check if the coercion holds.

Code

const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;

Example

validateNumber('10'); // true

Returns true if the string is y/yes or false if the string is n/no.

Use RegExp.test() to check if the string evaluates to y/yes or n/no. Omit the second argument, def to set the default answer as no.

Code

const yesNo = (val, def = false) =>
 /^(y|yes)$/i.test(val) ? true : /^(n|no)$/i.test(val) ? false : def;

Example

yesNo('Y'); // true
yesNo('yes'); // true
yesNo('No'); // false
yesNo('Foo', true); // true

at res quokka.js:1664:0