static

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。

 

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 (ECMA-262)
Class definitions
Living Standard  

浏览器兼容

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
staticChrome Full support 49
Full support 49
No support 42 — 49
Notes
Notes Strict mode is required.
No support 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.
Edge Full support 13Firefox Full support 45IE No support NoOpera Full support 36
Full support 36
No support 29 — 36
Notes
Notes Strict mode is required.
No support 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).
Safari Full support 9WebView Android Full support 49
Full support 49
No support 42 — 49
Notes
Notes Strict mode is required.
Chrome Android Full support 49
Full support 49
No support 42 — 49
Notes
Notes Strict mode is required.
No support 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.
Firefox Android Full support 45Opera Android Full support 36
Full support 36
No support 29 — 36
Notes
Notes Strict mode is required.
No support 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).
Safari iOS Full support 9Samsung Internet Android Full support 5.0
Full support 5.0
No support 4.0 — 5.0
Notes
Notes Strict mode is required.
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
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

相关链接