Map.@@species

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

Syntax

Map[Symbol.species]

Description

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

Examples

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

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

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	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'get Map [ @@species ]' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'get Map [ @@species ]' in that specification.	Draft

Browser compatibility

See also

• Map
• Symbol.species