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Spread operator

This is an experimental technology, part of the Harmony (ECMAScript 6) proposal.
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

Summary

The spread operator allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.

Syntax

function calls:

f(...iterableObj);

array literals:

[...iterableObj, 4, 5, 6]

Examples

A better apply

Example: it is common to use Function.prototype.apply in cases where you want to use an array as arguments to a function.

function f(x, y, z) { }
var args = [0, 1, 2];
f.apply(null, args);

With ES6 spread you can now write the above as:

function f(x, y, z) { }
var args = [0, 1, 2];
f(...args);

Any argument in the argument list can use the spread syntax and it can be used multiple times.

function f(v, w, x, y, z) { }
var args = [0, 1];
f(-1, ...args, 2, ...[3]);

A more powerful array literal

Example: Today if you have an array and want to create a new array with the existing one being part of it, the array literal syntax is no longer sufficient and you have to fall back to imperative code, using a combination of push, splice, concat, etc. With spread syntax this becomes much more succinct:

var parts = ['shoulder', 'knees'];
var lyrics = ['head', ...parts, 'and', 'toes'];

Just like with spread for argument lists ... can be used anywhere in the array literal and it can be used multiple times.

Apply for new

Example: In ES5 it is not possible to compose new with apply (in ES5 terms apply does a [[Call]] and not a [[Construct]]). In ES6 the spread syntax naturally supports this:

var dateFields = readDateFields(database);
var d = new Date(...dateFields);

A better push

Example: push is often used to push an array to the end of an existing array. In ES5 this is often done as:

var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
// Append all items from arr2 onto arr1
Array.prototype.push.apply(arr1, arr2);

In ES6 with spread this becomes:

var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1.push(...arr2);

Specifications

Specification Status Comment
EcmaScript Language Specification Draft 6th Edition Draft
  • 12.1.4 Array Initialiser
  • 12.2.6 Argument Lists

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Spread operation in array literals Not supported 16 (16) Not supported Not supported Not supported
Spread operation in function calls Not supported 27 (27) Not supported Not supported Not supported
Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Spread operation in array literals Not supported 16.0 (16) Not supported Not supported Not supported
Spread operation in function calls Not supported 27.0 (27) Not supported Not supported Not supported

See also

Document Tags and Contributors

 Contributors to this page: fscholz
 Last updated by: fscholz,