Update Object properties
// There is no native map to the Object object, but how about this:
var myObject = { 'a': 1, 'b': 2, 'c': 3 };
Object.keys(myObject).map(function(key, index) {
myObject[key] *= 2;
});
console.log(myObject);
// => { 'a': 2, 'b': 4, 'c': 6 }
// But you could easily iterate over an object using for ... in:
var myObject = { 'a': 1, 'b': 2, 'c': 3 };
for (var key in myObject) {
if (myObject.hasOwnProperty(key)) {
myObject[key] *= 2;
}
}
console.log(myObject);
// { 'a': 2, 'b': 4, 'c': 6 }
// A lot of people are mentioning that the previous methods do not return a new object, but rather operate on the object itself. For that matter I wanted to add another solution that returns a new object and leaves the original object as it is:
var myObject = { 'a': 1, 'b': 2, 'c': 3 };
// returns a new object with the values at each key mapped using mapFn(value)
function objectMap(object, mapFn) {
return Object.keys(object).reduce(function(result, key) {
result[key] = mapFn(object[key])
return result
}, {})
}
var newObject = objectMap(myObject, function(value) {
return value * 2
})
console.log(newObject);
// => { 'a': 2, 'b': 4, 'c': 6 }
console.log(myObject);
// => { 'a': 1, 'b': 2, 'c': 3 }
// How about a one liner with immediate variable assignment in plain JS (ES6 / ES2015) ?
// Making use of spread operator and computed key name syntax:
let newObj = Object.assign({}, ...Object.keys(obj).map(k => ({[k]: obj[k] * obj[k]})));
// Another version using reduce:
let newObj = Object.keys(obj).reduce((p, c) => ({...p, [c]: obj[c] * obj[c]}), {});
// First example as a function:
const oMap = (o, f) => Object.assign({}, ...Object.keys(o).map(k => ({ [k]: f(o[k]) })));
// To square each value you can call it like this:
let mappedObj = oMap(myObj, (x) => x * x);
// If you want to map a nested object recursively in a functional style, it can be done like this:
const sqrObjRecursive = obj =>
Object.keys(obj).reduce(
(newObj, key) =>
obj[key] && typeof obj[key] === "object"
? { ...newObj, [key]: sqrObjRecursive(obj[key]) } // recurse.
: { ...newObj, [key]: obj[key] * obj[key] }, // square val.
{}
);
// Or more imperatively, like this:
const sqrObjRecursive = obj => {
Object.keys(obj).forEach(key => {
if (typeof obj[key] === "object") obj[key] = sqrObjRecursive(obj[key]);
else obj[key] = obj[key] * obj[key];
});
return obj;
};
// Since ES7 / ES2016 you can use Object.entries() instead of Object.keys() e.g. like this:
let newObj = Object.assign(...Object.entries(obj).map(([k, v]) => ({[k]: v * v})));
// ES2019 might introduce Object.fromEntries(), which simplifies this even more:
let newObj = Object.fromEntries(Object.entries(([key, val]) => [k, v * v]));
// Inherited properties and the prototype chain:
// In some rare situation you may need to map a class-like object which holds properties of an inherited object on its prototype-chain. In such cases Object.keys() won't work, because Object.keys() does not enumerate inherited properties. If you need to map inherited properties, you should use for (key in myObj) {...}.
// Here is an example of an object which inherits the properties of another object and how Object.keys() doesn't work in such scenario.
const obj1 = { 'a': 1, 'b': 2, 'c': 3}
const obj2 = Object.create(obj1); // One of multiple ways to inherit an object in JS.
// Here you see how the properties of obj1 sit on the 'prototype' of obj2
console.log(obj2) // Prints: obj2.__proto__ = { 'a': 1, 'b': 2, 'c': 3}
console.log(Object.keys(obj2)); // Prints: an empty Array.
for (key in obj2) {
console.log(key); // Prints: 'a', 'b', 'c'
}
// However, please do me a favor and avoid inheritance. :-)
// No native methods, but lodash#mapValues will do the job brilliantly
_.mapValues({ 'a': 1, 'b': 2, 'c': 3} , function(num) { return num * 3; });
// → { 'a': 3, 'b': 6, 'c': 9 }