The Symbol.species well-known symbol 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 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:

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 Latest Draft (ECMA-262)
The definition of 'Symbol.species' in that specification.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support511441 No3810
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support Yes Yes1441 No3810

See also

Document Tags and Contributors

 Contributors to this page: fscholz, jameshkramer, gsathya, kdex, mata007, nilssolanki, arai
 Last updated by: fscholz,