The well-known symbol Symbol.species
specifies a function-valued property that the constructor function uses to create derived objects.
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Property attributes of Symbol.species |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
Description
The species accessor property allows subclasses to override the default constructor for objects.
Examples
You might want to return Array
objects in your derived array class MyArray
. For example, when using methods such as map()
that return the default constructor, you want these methods to return a parent Array
object, instead of the MyArray
object. The species symbol lets you do this:
class MyArray extends Array { // Overwrite species to the parent Array constructor static get [Symbol.species]() { return Array; } } var a = new MyArray(1,2,3); var mapped = a.map(x => x * x); console.log(mapped instanceof MyArray); // false console.log(mapped instanceof Array); // true
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Symbol.species' in that specification. |
Standard | Initial definition. |
ECMAScript Latest Draft (ECMA-262) The definition of 'Symbol.species' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | 51 | 14 | 41 | No | 38 | 10 |
Feature | Android webview | Chrome for Android | Edge mobile | Firefox for Android | Opera Android | iOS Safari | Samsung Internet |
---|---|---|---|---|---|---|---|
Basic support | Yes | Yes | 14 | 41 | 38 | 10 | Yes |