How to Get the Length of An Object

There are 2 ways to get the length of the list of keys of an object.

Object.keys

Object.keys gets the top level list of keys of an object and returns an array of them. For example:

const a = {foo: 1, bar: 2};
const length = Object.keys(a).length // 2

Object.getPropertyNames

Object.getPropertyNames also gets a list of all top level of keys of an object and return them as an array. For example:

const a = {foo: 1, bar: 2};
const length = Object.getOwnPropertyNames(a).length // 2

for…in Loop

There is a special loop for looping through the keys of an object. You can do the following:

const a = {foo: 1, bar: 2};
let keysCount = 0;
for (let key in a) {
    keysCount++;
}
console.log(keysCount) // 2