jayelbiz
12/10/2018 - 9:25 PM
Vanilla JavaScript Quick Reference / Cheatsheet
Vanilla JavaScript Quick Reference / Cheatsheet
## Vanilla JavaScript Quick Reference / Cheatsheet
Just migrated it from Codepen.io to markdown. Credit goes to David Conner.
Accessing Dom Elements
// Returns a reference to the element by its ID.
document.getElementById('someid');
// Returns an array-like object of all child elements which have all of the given class names.
document.getElementsByClassName('someclass');
// Returns an HTMLCollection of elements with the given tag name.
document.getElementsByTagName('LI');
// Returns the first element within the document that matches the specified group of selectors.
document.querySelector('.someclass');
// Returns a list of the elements within the document (using depth-first pre-order traversal of the document's nodes)
// that match the specified group of selectors.
document.querySelectorAll('div.note, div.alert');
Grab Children/Parent Node(s)
// Get child nodes
var stored = document.getElementById('someid');
var children = stored.childNodes;
// Get parent node
var parental = children.parentNode;
Create New DOM Elements
// create new elments
var newHeading = document.createElement('h1');
var newParagraph = document.createElement('p');
// create text nodes for new elements
var h1Text= document.createTextNode('This is a nice header text!');
var pText= document.createTextNode('This is a nice paragraph text!');
// attach new text nodes to new elements
newHeading.appendChild(h1Text);
newParagraph.appendChild(pText);
// elements are now created and ready to be added to the DOM.
Add Elements to the DOM
// grab element on page you want to add stuff to
var firstHeading = document.getElementById('firstHeading');
// add both new elements to the page as children to the element we stored in firstHeading.
firstHeading.appendChild(newHeading);
firstHeading.appendChild(newParagraph);
// can also insert before like so
// get parent node of firstHeading
var parent = firstHeading.parentNode;
// insert newHeading before FirstHeading
parent.insertBefore(newHeading, firstHeading);
Add Elements to the DOM cont.
Suppose you have the following HTML:
<div id='box1'>
<p>Some example text</p>
</div>
<div id='box2'>
<p>Some example text</p>
</div>
You can insert another snippet of HTML between #box1 and #box2:
var box2 = document.getElementById('box2');
box2.insertAdjacentHTML('beforebegin', '<div><p>This gets inserted.</p></div>');
// beforebegin - The HTML would be placed immediately before the element, as a sibling.
// afterbegin - The HTML would be placed inside the element, before its first child.
// beforeend - The HTML would be placed inside the element, after its last child.
// afterend - The HTML would be placed immediately after the element, as a sibling.
Add/Remove/Toggle/Check Classes
// grab element on page you want to use
var firstHeading = document.getElementById('firstHeading');
// will remove foo if it is a class of firstHeading
firstHeading.classList.remove('foo');
// will add the class 'anotherClass' if one does not already exist
firstHeading.classList.add('anotherclass');
// add or remove multiple classes
firstHeading.classList.add('foo', 'bar');
firstHeading.classList.remove('foo', 'bar');
// if visible class is set remove it, otherwise add it
firstHeading.classList.toggle('visible');
// will return true if it has class of 'foo' or false if it does not
firstHeading.classList.contains('foo');
Add/Remove Array Item
// create an empty array
var myArray = [];
// create array with items. Can store any type
var myOtherArray = [myArray, true, 'a random string'];
// call specific value in an array
myOtherArray[0];
// will return myArray
// change value for this item
myOtherArray[0] = false;
// will now return false
// add to end of array
myOtherArray[myOtherArray.length] = 'new stuff';
// will return the new item 'new stuff'
// or you can use push()
myOtherArray.push('new stuff');
// will return new length of array
// you can remove this last item by using pop()
myOtherArray.pop();
// will return the last item of the array and will have removed it from myOtherArray
// shift and unshift will do the same for the begging of the Array
myOtherArray.shift();
// will remove and return first item of array
myOtherArray.unshift(1,2);
// this will add 1 and 2 to beginning of array and return new length
// you can use delete keyword but turn value to undefine and not shorten length. so we use splice()
myOtherArray.splice(2, 1);
// this will remove and return the third item only.
// first arg is where to start and second is how many things to splice. this example is 1.
Add/Remove Object Properties
// create an object
var newObject = {};
// add a property to object
newObject.newPropName = 'super slick';
// or other syntax
newObject['other new prop name'] = 'mildly slick';
// Now newObject.newPropName will return 'super slick'
newObject.newPropName;
// now to delete
delete newObject.newPropName;
Conditionals
// If Else statements
var a = 1;
var b = 2;
if (a < b) {
console.log('the if is true!');
} else {
console.log('the if is false!');
}
// Multi If Else statements
var a = 1;
var b = 2;
var c = 3;
if (a > b) {
console.log('a is bigger than b');
} else if (a > c) {
console.log('but a is bigger than c');
} else {
console.log('a is the smallest');
}
// Ternary operators. same as if else
var a = 1;
var b = 2;
a === b ? console.log('The statement is true') : console.log('The statement is false');
// switch statements
var a = 4;
switch (a) {
case 'Oranges':
console.log('Orange? really?');
break;
case 1:
console.log('a is equal to 1.');
break;
case 2:
console.log('a is equal to 2.');
break;
case 3:
console.log('a is equal to 3.');
break;
case 4:
console.log('a is equal to 4.');
break;
default:
console.log('I run if no one else is true.');
}
Loops
// while loop
var i = 0;
while (i < 10) {
console.log(i);
i += 1
}
// do while loop
var i = 0;
do {
console.log(i);
i += 1
} while (i < 10)
// for loop
for (var i = 0; i < 10; i++) {
console.log(i);
}
// for in statments
var obj = {a:1, b:2, c:3};
for (var prop in obj) {
// check if property is inherited or not
if (obj.hasOwnProperty(prop)) {
console.log('obj.' + prop + ' = ' + obj[prop]);
}
}
Events (MDN Event reference)
var newElement = document.getElementsByTagName('h1');
newElement.onclick = function() {
console.log('clicked');
};
var logEventType = function(e) {
console.log('event type:', e.type);
};
newElement.addEventListener('focus', logEventType, false);
newElement.removeEventListener('focus', logEventType, false);
window.onload = function() {
console.log('Im loaded');
};
Timers
function simpleMessage() {
alert('This is just a simple alert');
}
// set time out
window.setTimeout(simpleMessage, 5000);
// if you wanted to clear the timer.
var timer = window.setTimeout(simpleMessage, 5000);
window.clearTimeout(timer);
// set interval. will repeat every 5000ms
window.setInterval(simpleMessage, 5000);
// if you wanted to clear the intervals.
var intervalHandler = window.setInterval(simpleMessage, 5000);
window.clearInterval(intervalHandle);
Type Checking
var myNumber = 1;
var myString = 'some Text';
var bools = true;
var myArray = [];
var myObj = {};
var notNumber = NaN;
var nullified = null;
var undef;
typeof myNumber;
// returns 'number'
typeof myString;
// returns 'string'
typeof bools;
// returns 'boolean'
typeof myArray;
// returns 'object'.
// Not super helpful so must check if it has length property to see if it is an array.
typeof myArray === 'object' && myArray.hasOwnProperty('length');
// returns true
typeof myObj;
// returns 'object'. Must do the same test as above but expect false back from check.
typeof notNumber;
// returns 'number'. this is confusing but returns this as NaN is part of the global Number object.
// must check if isNaN()
typeof notNumber === 'number' && isNaN(notNumber);
// returns true if type of is 'number' and is still NaN
typeof undef;
// returns 'undefined'
undef === undefined && typeof undef === 'undefined';
// returns 'true'
notDeclared === undefined;
// -> Uncaught ReferenceError: notDeclared is not defined
Add default arguments to a function
var myFunc = function (arg1='default argument one', arg2='default argument two') {
console.log(arg1 + " & " + arg2);
};
myFunc(undefined, 'and a new value'); // logs 'default argument one & and a new value'
Throttle or Debounce Functions Calls
var helpers = {
/**
* debouncing, executes the function if there was no new event in $wait milliseconds
* @param func
* @param wait
* @param scope
* @returns {Function}
*/
debounce: function(func, wait, scope) {
var timeout;
return function() {
var context = scope || this, args = arguments;
var later = function() {
timeout = null;
func.apply(context, args);
};
clearTimeout(timeout);
timeout = setTimeout(later, wait);
};
},
/**
* In case of a "storm of events", this executes once every $threshold
* @param fn
* @param threshold
* @param scope
* @returns {Function}
*/
throttle: function(fn, threshold, scope) {
threshold || (threshold = 250);
var last, deferTimer;
return function() {
var context = scope || this;
var now = +new Date, args = arguments;
if (last && now < last + threshold) {
// Hold on to it
clearTimeout(deferTimer);
deferTimer = setTimeout(function() {
last = now;
fn.apply(context, args);
}, threshold);
} else {
last = now;
fn.apply(context, args);
}
};
}
};
var resizeHandler = function(){
console.log('do stuff');
};
// Debounce by waiting 0.25s (250ms) with "this" context
window.addEventListener('resize', helpers.debounce(resizeHandler, 250, this));