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
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
@@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