Symbol.species
The well-known symbol Symbol.species
specifies a function-valued property that the constructor function uses to create derived objects.
Description
The species
accessor property allows subclasses to override the default constructor for objects.
Property attributes of Symbol.species |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
Examples
Using species
You might want to return Array
objects in your derived array class MyArray
. For example, when using methods such as map()
that return the default constructor, you want these methods to return a parent Array
object, instead of the MyArray
object. The species
symbol lets you do this:
class MyArray extends Array {
// Overwrite species to the parent Array constructor
static get [Symbol.species]() { return Array; }
}
let a = new MyArray(1,2,3);
let mapped = a.map(x => x * x);
console.log(mapped instanceof MyArray); // false
console.log(mapped instanceof Array); // true
Specifications
Specification |
---|
ECMAScript Language Specification # sec-symbol.species |
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