W3cubDocs

/JavaScript

Symbol.species

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

Using species

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; }
}
let a = new MyArray(1,2,3);
let mapped = a.map(x => x * x);

console.log(mapped instanceof MyArray); // false
console.log(mapped instanceof Array);   // true

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
species 51 13 41 No 38 10
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
species 51 51 41 41 10 5.0
Server
Node.js
species 6.5.0
6.5.0
6.0.0
Disabled
Disabled From version 6.0.0: this feature is behind the --harmony runtime flag.

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/species