The Symbol.hasInstance well-known symbol is used to determine if a constructor object recognizes an object as its instance. The instanceof operator's behavior can be customized by this symbol.

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

Examples

You could implement your custom instanceof behavior like this, for example:

class MyArray {  
  static [Symbol.hasInstance](instance) {
    return Array.isArray(instance);
  }
}
console.log([] instanceof MyArray); // true

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Symbol.hasInstance' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Symbol.hasInstance' in that specification.
Draft  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support511550 No Yes Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes Yes50 Yes Yes Yes

1. From version 6.0.0: this feature is behind the --harmony runtime flag.

See also

Document Tags and Contributors

Contributors to this page: wbamberg, fscholz, jameshkramer, kdex, GoToLoop, ZeikJT
Last updated by: wbamberg,