Web/JavaScript/Reference/Global objects/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

Specification
ECMAScript (ECMA-262)The definition of 'Symbol.species' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`species`	Chrome Full support 51	Edge Full support 13	Firefox Full support 41	IE No support No	Opera Full support 38	Safari Full support 10	WebView Android Full support 51	Chrome Android Full support 51	Firefox Android Full support 41	Opera Android Full support 41	Safari iOS Full support 10	Samsung Internet Android Full support 5.0	nodejs 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.