Map[@@species]
The Map[@@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 @@species
was called. The return value is used to construct copied Map
instances.
Description
The @@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 @@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 Language Specification # sec-get-map-@@species |
Browser compatibility
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