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Symbol.species

The well-known symbol Symbol.species specifies a function-valued property that the constructor function uses to create derived objects.

Property attributes of Symbol.species
Writable no
Enumerable no
Configurable no

Description

The species accessor property allows subclasses to override the default constructor for objects.

Examples

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; }
}
var a = new MyArray(1,2,3);
var mapped = a.map(x => x * x);

console.log(mapped instanceof MyArray); // false
console.log(mapped instanceof Array);   // true

Specifications

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 51 14 41 No 38 10
Feature Android webview Chrome for Android Edge mobile Firefox for Android Opera Android iOS Safari Samsung Internet
Basic support Yes Yes 14 41 38 10 ?

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/species