Symbol.species
The Symbol.species
well-known symbol specifies a function valued property that is the constructor function that is used to create derived objects.
Property attributes of Symbol.species |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
Description
The species accessor property allows subclasses to over-ride 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:
JavaScript
Copy Code
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
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Symbol.species' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Symbol.species' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 51 | 41 (41) | No support | No support | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | 5 | 41.0 (41) | No support | No support | No support |
See also
License
© 2016 Mozilla 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