类（class）通过 static 关键字定义静态方法。不能在类的实例上调用静态方法，而应该通过类本身调用。这些通常是实用程序方法，例如创建或克隆对象的功能。

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## 语法

    static methodName() { ... }

## 描述

静态方法调用直接在类上进行，不能在类的实例上调用。静态方法通常用于创建实用程序函数。

## 调用静态方法

### 从另一个静态方法

静态方法调用同一个类中的其他静态方法，可使用 `this` 关键字。

    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'

### 从类的构造函数和其他方法

非静态方法中，不能直接使用 `this` 关键字来访问静态方法。而是要用类名来调用：`CLASSNAME.STATIC_METHOD_NAME()` ，或者用构造函数的属性来调用该方法： `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.';
        }
    }

## 示例

下面的例子说明了这几点：

1. 静态方法如何在类上实现。
2. 具有静态成员的类，可以被子类化 。
3. 什么情况下静态方法可以调用，什么情况下不能调用。

    class Tripple {
      static tripple(n = 1) {
        return n * 3;
      }
    }

    class BiggerTripple extends Tripple {
      static tripple(n) {
        return super.tripple(n) * super.tripple(n);
      }
    }

    console.log(Tripple.tripple());// 3
    console.log(Tripple.tripple(6));// 18

    let tp = new Tripple();

    console.log(BiggerTripple.tripple(3));// 81（不会受父类实例化的影响）
    console.log(tp.tripple());// 'tp.tripple 不是一个函数'.

## 规范

Specification | Status | Comment
--- | --- | ---
ECMAScript 2015 (6th Edition, ECMA-262) Class definitions | Standard | Initial definition.
ECMAScript Latest Draft (ECMA-262) Class definitions | Draft |

## 浏览器兼容

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.

Update compatibility data on GitHub

| Desktop | Mobile | Server
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | Safari on iOS | Samsung Internet | Node.js
`static` | Chrome Full support 49 Notes Full support 49 Notes Notes From Chrome 42 to 48 strict mode is required. Non-strict mode support can be enabled using the flag "Enable Experimental JavaScript". | Edge Full support 13 | Firefox Full support 45 | IE No support No | Opera Full support 36 | Safari Full support 9 | WebView Android ? | Chrome Android Full support Yes | Edge Mobile Full support 13 | Firefox Android Full support 45 | Opera Android ? | Safari iOS Full support 9 | Samsung Internet Android Full support Yes | nodejs Full support 6.0.0 Full support 6.0.0 Full support 4.0.0 Disabled Disabled From version 4.0.0: this feature is behind the `--use_strict` runtime flag. Full support 5.0.0 Disabled Disabled From version 5.0.0: this feature is behind the `--harmony` runtime flag.

### Legend

Full support
  Full support
No support
  No support
Compatibility unknown
  Compatibility unknown
See implementation notes.
  See implementation notes.
User must explicitly enable this feature.
  User must explicitly enable this feature.

## 相关链接

- `class`表达式
- `class`声明
- Classes