Multiple assignment in javascript? What does [a,b,c] = [1, 2, 3]; mean?

Question

For a project a developer sent us a .js file with code similar to this:

var myList = [1,2,3]; var a,b,c;  [a,b,c] = myList; 

It works in Opera 10.30, Firefox 3.6.x but it's not ok for Opera 10.60 and Chrome.

It's just curiosity, do you have any reference or link that says this code is compliant to JS/ECMA standard or not?

What do you think?

Answer 1

This is a feature called destructuring assignment, which was added in JavaScript 1.7 and ECMAScript 6. It is not a part of ECMAScript 5: What is cross browser support for JavaScript 1.7's new features? Specifically array comprehensions and the "let" statement

Answer 2

Here’s an update on the subject: as of JavaScript version 1.7, destructuring assignments are supported by all major browsers: see browser compatibility.

The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from objects, into distinct variables.

– MDN’s documentation

So you can do:

let a, b; [a, b] = ["Hello", "World"];  console.log(a); // "Hello" console.log(b); // "World" 

Or simply in one line if you're defining the variables:

let [a, b] = ["Hello", "World"];  console.log(a); // "Hello" console.log(b); // "World"