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static

The static keyword defines a static method or property for a class. Neither static methods nor static properties can be called on instances of the class. Instead, they're called on the class itself. Static methods are often utility functions, such as functions to create or clone objects, whereas static properties are useful for caches, fixed-configuration, or any other data you don't need to be replicated across instances.

Syntax

static methodName() { ... }
static propertyName [= value];

Examples

Using static members in classes

The following example demonstrates several things:

  1. How a static member (method or property) is defined on a class.
  2. That a class with a static member can be sub-classed.
  3. How a static member can and cannot be called.
class Triple {
  static customName = 'Tripler';
  static description = 'I triple any number you provide';
  static triple(n = 1) {
    return n * 3;
  }
}

class BiggerTriple extends Triple {
  static longDescription;
  static description = 'I square the triple of any number you provide';
  static triple(n) {
    return super.triple(n) * super.triple(n);
  }
}

console.log(Triple.description);   // 'I triple any number you provide'
console.log(Triple.triple());      // 3
console.log(Triple.triple(6));     // 18

var tp = new Triple();

console.log(BiggerTriple.triple(3));        // 81 (not affected by parent's instantiation)
console.log(BiggerTriple.description);      // 'I square the triple of any number you provide'
console.log(BiggerTriple.longDescription);  // undefined
console.log(BiggerTriple.customName);       // 'Tripler'

console.log(tp.triple());         // 'tp.triple is not a function'.

Calling static members from another static method

In order to call a static method or property within another static method of the same class, you can use the this keyword.

class StaticMethodCall {
  static staticProperty = 'static property';
  static staticMethod() {
    return 'Static method and ' + this.staticProperty + ' has been called';
  }
  static anotherStaticMethod() {
    return this.staticMethod() + ' from another static method';
  }
}
StaticMethodCall.staticMethod(); 
// 'Static method and static property has been called'

StaticMethodCall.anotherStaticMethod(); 
// 'Static method and static property has been called from another static method'

Calling static members from a class constructor and other methods

Static members are not directly accessible using the this keyword from non-static methods. You need to call them using the class name: CLASSNAME.STATIC_METHOD_NAME() / CLASSNAME.STATIC_PROPERTY_NAME or by calling the method as a property of the constructor: this.constructor.STATIC_METHOD_NAME() / this.constructor.STATIC_PROPERTY_NAME

class StaticMethodCall {
  constructor() {
    console.log(StaticMethodCall.staticProperty); // 'static property'
    console.log(this.constructor.staticProperty); // 'static property' 
    console.log(StaticMethodCall.staticMethod()); // 'static method has been called.' 
    console.log(this.constructor.staticMethod()); // 'static method has been called.' 
  }
 
  static staticProperty = 'static property';
  static staticMethod() {
    return 'static method has been called.';
  }
}

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
static 49
49
42 — 49
Strict mode is required.
42 — 49
Disabled
Disabled From version 42 until version 49 (exclusive): this feature is behind the Experimental JavaScript preference (needs to be set to Enabled). To change preferences in Chrome, visit chrome://flags.
13 45 No 36
36
29 — 36
Strict mode is required.
29 — 36
Disabled
Disabled From version 29 until version 36 (exclusive): this feature is behind the Experimental JavaScript preference (needs to be set to Enabled).
9
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
static 49
49
42 — 49
Strict mode is required.
49
49
42 — 49
Strict mode is required.
42 — 49
Disabled
Disabled From version 42 until version 49 (exclusive): this feature is behind the Experimental JavaScript preference (needs to be set to Enabled). To change preferences in Chrome, visit chrome://flags.
45 36
36
29 — 36
Strict mode is required.
29 — 36
Disabled
Disabled From version 29 until version 36 (exclusive): this feature is behind the Experimental JavaScript preference (needs to be set to Enabled).
9 5.0
5.0
4.0 — 5.0
Strict mode is required.
Server
Node.js
static 6.0.0
6.0.0
4.0.0
Disabled
Disabled From version 4.0.0: this feature is behind the --use_strict runtime flag.
5.0.0
Disabled
Disabled From version 5.0.0: this feature is behind the --harmony runtime flag.

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static