The @@unscopables
data property contains property names that were not included in the ECMAScript standard prior to the ES2015 version and that are ignored for with
statement-binding purposes.
Array.prototype[@@unscopables]
Description
The default Array
properties that are ignored for with
statement-binding purposes 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 |
Example
Imagine the keys.push('something')
call below is in code that was written prior to ECMAScript 2015.
When ECMAScript 2015 introduced the Array.prototype.keys()
method, if the @@unscopables
data property had not also been introduced, that keys.push('something')
call would break — because the JavaScript runtime would have interpreted keys
as being the Array.prototype.keys()
method, rather than the keys
array defined in the example code.
So the @@unscopables
data property for Array.prototype
causes the Array
properties introduced in ECMAScript 2015 to be ignored for with
statement-binding purposes — allowing code that was written prior to ECMAScript 2015 to continue working as expected, rather than breaking.
var keys = []; with (Array.prototype) { keys.push('something'); } Object.keys(Array.prototype[Symbol.unscopables]); // ["at", "copyWithin", "entries", "fill", "find", "findIndex", // "includes", "keys", "values"]
Specifications
Browser compatibility
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
@@unscopables |
38
|
12
|
48
|
No
|
25
|
10
|
38
|
38
|
48
|
25
|
10
|
3.0
|
1.0
|
0.12.0
|
See also
© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/@@unscopables