Map[Symbol.species]

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The Map[Symbol.species] static accessor property is an unused accessor property specifying how to copy Map objects.

Syntax

js
Map[Symbol.species]

Return value

The value of the constructor (this) on which get [Symbol.species] was called. The return value is used to construct copied Map instances.

Description

The [Symbol.species] accessor property returns the default constructor for Map objects. Subclass constructors may override it to change the constructor assignment.

Note: This property is currently unused by all Map methods.

Examples

Species in ordinary objects

The [Symbol.species] property returns the default constructor function, which is the Map constructor for Map.

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

Species in derived objects

In an instance of a custom Map subclass, such as 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:

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

Specifications

Specification
ECMAScript® 2025 Language Specification
# sec-get-map-%symbol.species%

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
[Symbol.species]

Legend

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Full support
Full support

See also