EventEmitter.call（）做什么？ [英] What does EventEmitter.call() do?

问题描述

我看到了这个代码示例：

I saw this code sample:

function Dog(name) {
    this.name = name;
    EventEmitter.call(this);
}

它从EventEmitter继承，但call（）方法实际上是什么吗？

it 'inherits' from EventEmitter, but what does the call() method actually do?

推荐答案

基本上， Dog 应该是带有属性的构造函数名称。 EventEmitter.call（this），在 Dog 实例创建期间执行时，附加从<$ c $声明的属性c> EventEmitter 构造函数到 Dog 。

Basically, Dog is supposedly a constructor with a property name. The EventEmitter.call(this), when executed during Dog instance creation, appends properties declared from the EventEmitter constructor to Dog.

请记住：构造函数仍然是函数，并且仍然可以用作函数。

Remember: constructors are still functions, and can still be used as functions.

//An example EventEmitter
function EventEmitter(){
  //for example, if EventEmitter had these properties
  //when EventEmitter.call(this) is executed in the Dog constructor
  //it basically passes the new instance of Dog into this function as "this"
  //where here, it appends properties to it
  this.foo = 'foo';
  this.bar = 'bar';
}

//And your constructor Dog
function Dog(name) {
    this.name = name;
    //during instance creation, this line calls the EventEmitter function
    //and passes "this" from this scope, which is your new instance of Dog
    //as "this" in the EventEmitter constructor
    EventEmitter.call(this);
}

//create Dog
var newDog = new Dog('furball');
//the name, from the Dog constructor
newDog.name; //furball
//foo and bar, which were appended to the instance by calling EventEmitter.call(this)
newDog.foo; //foo
newDoc.bar; //bar

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