Using Square Brackets in Object Literal Keys

It may be difficult to understand how keys can be assigned using square brackets within an object literal. Let's dive into the explanation behind this ES2015 syntax.

The code snippet you provided:

let a = "b"
let c = {[a]: "d"}

uses the computed property name syntax, which is a shorthand for the traditional ES3/5 someObject[someKey] assignment. In other words, it expands to:

var a = "b"
var c = {}
c[a] = "d"

This syntax allows you to dynamically generate property names based on variables or expressions, providing greater flexibility in object construction. When using this feature, ensure that the property name is enclosed in square brackets, as in [a] in the example.