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.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Property attributes of Symbol.hasInstance |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
Examples
Custom instanceof behavior
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
function MyArray() { } Object.defineProperty(MyArray, Symbol.hasInstance, { value: function(instance) { return Array.isArray(instance); } }); console.log([] instanceof MyArray); // true
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Symbol.hasInstance' in that specification. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
hasInstance | Chrome Full support 50 | Edge Full support 15 | Firefox Full support 50 | IE No support No | Opera Full support 37 | Safari Full support 10 | WebView Android Full support 50 | Chrome Android Full support 50 | Firefox Android Full support 50 | Opera Android Full support 37 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs
Full support
6.5.0
|
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.