The Symbol.unscopables well-known symbol is used to specify an object value of whose own and inherited property names are excluded from the with environment bindings of the associated object.


The @@unscopables symbol (Symbol.unscopables) can be defined on any object to exclude property names from being exposed as lexical variables in with with environment bindings. Note that if using Strict mode, with statements are not available and will likely also not need this symbol.

Setting a property to true in an unscopables object will make it unscopable and therefore it won't appear in lexical scope variables. Setting a property to false will make it scopable and thus it will appear in lexical scope variables.

Property attributes of Symbol.unscopables
Writable no
Enumerable no
Configurable no


Scoping in with statements

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 environment "keys" would now be the method and not the variable. That's when the unscopables symbol was introduced. A built-in unscopables setting is implemented as Array.prototype[@@unscopables] to prevent that some of the Array methods are being scoped into the with statement.

var keys = [];

with (Array.prototype) {

// ["copyWithin", "entries", "fill", "find", "findIndex", 
//  "includes", "keys", "values"]

Unscopables in objects

You can also set unscopables for your own objects.

var obj = { 
  foo: 1, 
  bar: 2 

obj[Symbol.unscopables] = { 
  foo: false, 
  bar: true 

with (obj) {
  console.log(foo); // 1
  console.log(bar); // ReferenceError: bar is not defined


ECMAScript (ECMA-262)
The definition of 'Symbol.unscopables' in that specification.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
unscopablesChrome Full support 45Edge Full support 12Firefox Full support 48IE No support NoOpera Full support 32Safari Full support 9WebView Android Full support 45Chrome Android Full support 45Firefox Android Full support 48Opera Android Full support 32Safari iOS Full support 9Samsung Internet Android Full support 5.0nodejs Full support 0.12


Full support  
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See also