如何在不实例化的情况下从类调用方法? [英] How can I call a method from a class without instantiating it?

问题描述

如果你看看像 cocos2d-x 这样的框架，例如:

If you look at a framework like cocos2d-x, for example:

cc.Sprite.extend();

这里的 Sprite 是一个类；如何在不使用 new 关键字实例化的情况下调用其方法之一?

Sprite here is a class; how can I call one of its methods without instantiating it with the new keyword?

例如，如果我有这个类:

For example, if I have this class:

var superClass = function(){
    
    this.init = function(){
        console.log("new class constructed !")
    };

};

要调用init，我必须这样做:

To call init, I must do this:

obj = new superClass();
obj.init();

但是如何在不需要实例化类的情况下调用函数?

But how can I call the function without needing to instantiate the class?

推荐答案

ES6 及更新版本:

使用static 关键字.大多数现代浏览器都支持它.

class SuperClass {
   static init() {
     console.log("new class constructed !")
   }
}

SuperClass.init();

旧版浏览器:

有不同的方法可以实现这一目标.一种选择是使用对象字面量.

Older browsers:

There are different ways to achieve that. One option is to use an object literal.

对象字面量:

var superClass = {
    init: function(){
        console.log("new class constructed !")
    }
};

superClass.init();

https://jsfiddle.net/ckgmb9fk/

但是，您仍然可以使用函数构造函数定义对象，然后向类"添加静态方法.例如，您可以这样做:

However, you can still define an object using a function constructor and then add a static method to the "class". For example, you can do this:

var SuperClass = function(){};

SuperClass.prototype.methodA = function() {
    console.log("methodA");
};

SuperClass.init = function() {
    console.log("Init function");
}

SuperClass.init();

var sc = new SuperClass();
sc.methodA();

请注意，方法 init 在 SuperClass 实例对象中将不可用，因为它不在对象原型中.

Note that the method init won't be available in the SuperClass instance object because it is not in the object prototype.

https://jsfiddle.net/mLxoh1qj/

扩展原型:

var SuperClass = function(){};

  SuperClass.prototype.init = function() {
      console.log("Init");
  };

SuperClass.prototype.init();

var sc = new SuperClass();
sc.init();

https://jsfiddle.net/0ayct1ry/

如果您想从 SuperClass 原型和对象实例访问函数 init，此解决方案很有用.

This solution is useful if you want to access the function init both from the SuperClass prototype and from an object instance.

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