Map[Symbol.species] - JavaScript | MDN
Syntax
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® 2027 Language Specification # sec-get-map-%symbol.species% |