static
keyword defines a static method for a class. Static methods aren't called on instances of the class. Instead, they're called on the class itself.
These are often utility functions, such as functions to create or clone objects.
static methodName() { ... }
The following example demonstrates several things:
class Triple {
static triple(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
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'.
In order to call a static method within another static method of the same class, you can use the
this
关键词。
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'
Static methods 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()
or by calling the method as a property of the
构造函数
:
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.';
}
}
| 规范 |
|---|
|
ECMAScript (ECMA-262)
The definition of 'Class definitions' in that specification. |
| Desktop | Mobile | Server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
static
|
Chrome
49
|
Edge 13 | Firefox 45 | IE No |
Opera
36
|
Safari 9 |
WebView Android
49
|
Chrome Android
49
|
Firefox Android 45 |
Opera Android
36
|
Safari iOS 9 |
Samsung Internet Android
5.0
|
nodejs
6.0.0
|
完整支持
不支持
见实现注意事项。
用户必须明确启用此特征。