Spread syntax allows an iterable such as an array expression or string to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected, or an object expression to be expanded in places where zero or more key-value pairs (for object literals) are expected.

Syntax

For function calls:

myFunction(...iterableObj);

For array literals or strings:

[...iterableObj, '4', 'five', 6];

For object literals (new in ECMAScript 2018):

let objClone = { ...obj };

Examples

Spread in function calls

Replace apply

It is common to use Function.prototype.apply in cases where you want to use the elements of an array as arguments to a function.

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

With spread syntax the above can be written as:

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

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

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

Apply for new

When calling a constructor with new, it's not possible to directly use an array and apply (apply does a [[Call]] and not a [[Construct]]). However, an array can be easily used with new thanks to spread syntax:

var dateFields = [1970, 0, 1];  // 1 Jan 1970
var d = new Date(...dateFields);

To use new with an array of parameters without spread syntax, you would have to do it indirectly through partial application:

function applyAndNew(constructor, args) {
   function partial () {
      return constructor.apply(this, args);
   };
   if (typeof constructor.prototype === "object") {
      partial.prototype = Object.create(constructor.prototype);
   }
   return partial;
}


function myConstructor () {
   console.log("arguments.length: " + arguments.length);
   console.log(arguments);
   this.prop1="val1";
   this.prop2="val2";
};

var myArguments = ["hi", "how", "are", "you", "mr", null];
var myConstructorWithArguments = applyAndNew(myConstructor, myArguments);

console.log(new myConstructorWithArguments);
// (internal log of myConstructor):           arguments.length: 6
// (internal log of myConstructor):           ["hi", "how", "are", "you", "mr", null]
// (log of "new myConstructorWithArguments"): {prop1: "val1", prop2: "val2"}

Spread in array literals

A more powerful array literal

Without spread syntax, to create a new array using an existing array as one part of it, the array literal syntax is no longer sufficient and imperative code must be used instead using a combination of push, splice, concat, etc. With spread syntax this becomes much more succinct:

var parts = ['shoulders', 'knees']; 
var lyrics = ['head', ...parts, 'and', 'toes']; 
// ["head", "shoulders", "knees", "and", "toes"]

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

Copy an array

var arr = [1, 2, 3];
var arr2 = [...arr]; // like arr.slice()
arr2.push(4); 

// arr2 becomes [1, 2, 3, 4]
// arr remains unaffected

Note: Spread syntax effectively goes one level deep while copying an array. Therefore, it may be unsuitable for copying multidimensional arrays as the following example shows (it's the same with Object.assign() and spread syntax).

var a = [[1], [2], [3]];
var b = [...a];
b.shift().shift(); // 1
// Now array a is affected as well: [[], [2], [3]]

A better way to concatenate arrays

Array.concat is often used to concatenate an array to the end of an existing array. Without spread syntax this is done as:

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

With spread syntax this becomes:

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

Array.unshift is often used to insert an array of values at the start of an existing array.  Without spread syntax this is done as:

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

With spread syntax this becomes [Note, however, that this creates a new arr1 array. Unlike Array.unshift, it does not modify the original arr1 array in-place]:

var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1 = [...arr2, ...arr1]; // arr1 is now [3, 4, 5, 0, 1, 2]

Spread in object literals

The Rest/Spread Properties for ECMAScript proposal (stage 4) adds spread properties to object literals. It copies own enumerable properties from a provided object onto a new object.

Shallow-cloning (excluding prototype) or merging of objects is now possible using a shorter syntax than Object.assign().

var obj1 = { foo: 'bar', x: 42 };
var obj2 = { foo: 'baz', y: 13 };

var clonedObj = { ...obj1 };
// Object { foo: "bar", x: 42 }

var mergedObj = { ...obj1, ...obj2 };
// Object { foo: "baz", x: 42, y: 13 }

Note that Object.assign() triggers setters whereas spread syntax doesn't.

Note that you cannot replace nor mimic the Object.assign() function:

var obj1 = { foo: 'bar', x: 42 };
var obj2 = { foo: 'baz', y: 13 };
const merge = ( ...objects ) => ( { ...objects } );

var mergedObj = merge ( obj1, obj2);
// Object { 0: { foo: 'bar', x: 42 }, 1: { foo: 'baz', y: 13 } }

var mergedObj = merge ( {}, obj1, obj2);
// Object { 0: {}, 1: { foo: 'bar', x: 42 }, 2: { foo: 'baz', y: 13 } }

In the above example, the spread syntax does not work as one might expect: it spreads an array of arguments into the object literal, due to the rest parameter.

Only for iterables

Spread syntax (other than in the case of spread properties) can be applied only to iterable objects:

var obj = {'key1': 'value1'};
var array = [...obj]; // TypeError: obj is not iterable

Spread with many values

When using spread syntax for function calls, be aware of the possibility of exceeding the JavaScript engine's argument length limit. See apply() for more details.

Rest syntax (parameters)

Rest syntax looks exactly like spread syntax, but is used for destructuring arrays and objects. In a way, rest syntax is the opposite of spread syntax: spread 'expands' an array into its elements, while rest collects multiple elements and 'condenses' them into a single element. See rest parameters.

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262) Standard Defined in several sections of the specification: Array Initializer, Argument Lists
ECMAScript 2018 (ECMA-262) Standard Defined in Object Initializer
ECMAScript Latest Draft (ECMA-262) Draft No changes.
ECMAScript Latest Draft (ECMA-262) Draft No changes.

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
Spread in array literalsChrome Full support 46Edge Full support 12Firefox Full support 16IE No support NoOpera Full support 37Safari Full support 8WebView Android Full support 46Chrome Android Full support 46Edge Mobile Full support 12Firefox Android Full support 16Opera Android Full support 37Safari iOS Full support 8Samsung Internet Android Full support 5.0nodejs Full support 5.0.0
Full support 5.0.0
Full support 4.0.0
Disabled
Disabled From version 4.0.0: this feature is behind the --harmony runtime flag.
Spread in function callsChrome Full support 46Edge Full support 12Firefox Full support 27IE No support NoOpera Full support 37Safari Full support 8WebView Android Full support 46Chrome Android Full support 46Edge Mobile Full support 12Firefox Android Full support 27Opera Android Full support 37Safari iOS Full support 8Samsung Internet Android Full support 5.0nodejs Full support 5.0.0
Full support 5.0.0
Full support 4.0.0
Disabled
Disabled From version 4.0.0: this feature is behind the --harmony runtime flag.
Spread in destructuringChrome Full support 49Edge No support NoFirefox Full support 34IE No support NoOpera Full support 37Safari ? WebView Android Full support 49Chrome Android Full support 49Edge Mobile No support NoFirefox Android Full support 34Opera Android Full support 37Safari iOS ? Samsung Internet Android Full support 5.0nodejs Full support Yes
Spread in object literals
Experimental
Chrome Full support 60Edge No support NoFirefox Full support 55IE No support NoOpera ? Safari No support NoWebView Android Full support 60Chrome Android Full support 60Edge Mobile No support NoFirefox Android Full support 55Opera Android ? Safari iOS No support NoSamsung Internet Android No support Nonodejs Full support 8.3.0
Full support 8.3.0
Full support 8.0.0
Disabled
Disabled From version 8.0.0: this feature is behind the --harmony runtime flag.

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also

Document Tags and Contributors

Last updated by: KadirTopal,