Web/JavaScript/Reference/Global objects/Map/@@species

The Map[@@species] accessor property returns the Map constructor.

Description

The species accessor property returns the default constructor for Map objects. Subclass constructors may over-ride it to change the constructor assignment.

Examples

Species in ordinary objects

The species property returns the default constructor function, which is the Map constructor for Map objects:

Map[Symbol.species]; // function Map()

Species in derived objects

In a derived collection object (e.g. your custom map MyMap), the MyMap species is the MyMap constructor. However, you might want to overwrite this, in order to return parent Map objects in your derived class methods:

class MyMap extends Map {
  // Overwrite MyMap species to the parent Map constructor
  static get [Symbol.species]() { return Map; }
}

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'get Map [ @@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.