static 不被实例调用

static - JavaScript | MDN https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static

The 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.

Link to sectionSyntax

static methodName() { ... }

Link to sectionDescription

Static method calls are made directly on the class and are not callable on instances of the class. Static methods are often used to create utility functions.

Link to sectionCalling static methods

Link to sectionFrom 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'

　　

Link to sectionFrom class constructor and other methods

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 theconstructor: 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.';
  }
}

　　

Link to sectionExamples

The following example demonstrates several things:

1. How a static method is implemented on a class.
2. That a class with a static member can be sub-classed.
3. 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

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'.