arrays - Object properties in JavaScript

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65920091/object-properties-in-javascript

Answer 1

In JavaScript, [] is used to determine an Array literal, but is also one of the ways to call Object keys, hence your confusion.

const myArray = []; // Returns an empty array
const someObjectValue = myObject["myKey"] // returns the value of an object's key

Please note you can also fetch an object value by using dot instead of brackets:

// They are the same thing.
const value = myObject["myKey"];
const sameValue = myObject.myKey;

They're basically two different ways of achieving the same thing.

There is one difference, thought. With brackets you can assign otherwise non-allowed keys to objects.

Example:

const myObject = {};

// Set
myObject.0 = "Hello!"; // throws error
myObject[0] = "Hello!"; // works!

myObject.some-key = "Hello!"; // throws error
myObject["some-key"] = "Hello!"; // works!

// Get
const value = myObject.0; // throws error
const value = myObject[0]; // works!

const value = myObject.some-key; // throws error
const value = myObject["some-key"]; // works!