Web/JavaScript/Reference/Global objects/Array/@@unscopables

The @@unscopable symbol property contains property names that were not included in the ECMAScript standard prior to the ES2015 version. These properties are excluded from with statement bindings.

Description

The default array properties that are excluded from with bindings are:

See Symbol.unscopables for how to set unscopables for your own objects.

Property attributes of `Array.prototype[@@unscopables]`
Writable	no
Enumerable	no
Configurable	yes

Examples

Use in with environments

The following code works fine in ES5 and below. However, in ECMAScript 2015 and later, the Array.prototype.keys() method was introduced. That means that inside with environments, "keys" would now be the method and not the variable. This is where now the built-in @@unscopables Array.prototype[@@unscopables] symbol property comes into play and prevents that some of the Array methods are being scoped into the with statement.

var keys = [];

with (Array.prototype) {
  keys.push('something');
}

Object.keys(Array.prototype[Symbol.unscopables]); 
// ["copyWithin", "entries", "fill", "find", "findIndex", 
//  "includes", "keys", "values"]

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Array.prototype[@@unscopables' in that specification.]

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`@@unscopables`	Chrome Full support 38	Edge Full support 12	Firefox Full support 48	IE No support No	Opera Full support 25	Safari Full support 10	WebView Android Full support 38	Chrome Android Full support 38	Firefox Android Full support 48	Opera Android Full support 25	Safari iOS Full support 10	Samsung Internet Android Full support 3.0	nodejs Full support 0.12

Legend

Full support: Full support
No support: No support