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The static keyword defines a static method for a class.
Syntax
static methodName() { ... }
Description
Static methods are called without instantiating their class and are also not callable when the class is instantiated. Static methods are often used to create utility functions for an application.
Calling static methods
From another static method
In order to call a static method within another static method of the same class, you can use the this
keyword.
class StaticMethodCall { static staticMethod() { return 'Static method has been called'; } static anotherStaticMethod() { return this.staticMethod() + ' from another static method'; } } StaticMethodCall.staticMethod(); // 'Static method has been called' StaticMethodCall.anotherStaticMethod(); // 'Static method has been called from another static method'
From class constructor and other methods
Static methods are not directly accessible using just the this
keyword. You need to call them by using the class name in front: CLASSNAME.STATIC_METHOD_NAME
(like other calls from outside of class) or by using the constructor
property: this.constructor.STATIC_METHOD_NAME
.
class StaticMethodCall{ constructor(){ console.log(StaticMethodCall.staticMethod()); // 'static method has been called' console.log(this.constructor.staticMethod()); // 'static method has been called' } static staticMethod(){ return 'static method has been called.'; } }
Examples
The following example demonstrates several things. It shows how a static method is implemented on a class and that a class with a static member can be sub-classed. Finally it shows how a static method can and cannot be called.
class Triple { static triple(n) { if (n === undefined) { n = 1; } return n * 3; } } class BiggerTriple extends Triple { static triple(n) { return super.triple(n) * super.triple(n); } } console.log(Triple.triple()); // 3 console.log(Triple.triple(6)); // 18 console.log(BiggerTriple.triple(3)); // 81 var tp = new Triple(); console.log(BiggerTriple.triple(3)); // 81 (not affected by parent's instantiation) console.log(tp.triple()); // 'tp.triple is not a function'.
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Class definitions' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Class definitions' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 42.0 | 45 (45) | ? | ? | ? |
Feature | Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|
Basic support | No support | 45.0 (45) | ? | ? | ? | 42.0 |