Javascript object bracket notation ({ Navigation } =) on left side of assign

I haven’t seen this syntax before and am wondering what it’s all about.

var { Navigation } = require('react-router');

The brackets on the left are throwing a syntax error:

unexpected token {

I’m not sure what part of the webpack config is transforming or what the purpose of the syntax is. Is it a Harmony thing? Can someone enlighten me?

Answer

It’s called destructuring assignment and it’s part of the ES2015 standard.

The destructuring assignment syntax is a JavaScript expression that makes it possible to extract data from arrays or objects using a syntax that mirrors the construction of array and object literals.

Source: Destructuring assignment reference on MDN

Object destructuring

 var o = {p: 42, q: true};
 var {p, q} = o;

 console.log(p); // 42
 console.log(q); // true 

 // Assign new variable names
 var {p: foo, q: bar} = o;

 console.log(foo); // 42
 console.log(bar); // true

Array destructuring

var foo = ["one", "two", "three"];

// without destructuring
var one   = foo[0];
var two   = foo[1];
var three = foo[2];

// with destructuring
var [one, two, three] = foo;