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The well-known symbol Symbol.species specifies a function-valued property that the constructor function uses to create derived objects.

Description

The species accessor property allows subclasses to override the default constructor for objects.

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

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

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
speciesChrome Full support 51Edge Full support 13Firefox Full support 41IE No support NoOpera Full support 38Safari Full support 10WebView Android Full support 51Chrome Android Full support 51Edge Mobile Full support 14Firefox Android Full support 41Opera Android Full support 41Safari iOS Full support 10Samsung Internet Android Full support Yesnodejs Full support 6.5.0
Full support 6.5.0
Full support 6.0.0
Disabled
Disabled From version 6.0.0: this feature is behind the --harmony runtime flag.

Legend

Full support  
Full support
No support  
No support
User must explicitly enable this feature.
User must explicitly enable this feature.

See also

Document Tags and Contributors

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