EventEmitter.call（）是做什么的？

Question

我看到这个代码示例：

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

它继承“从EventEmitter，但到底是什么（）的调用方法实际上呢？

Answer 1

基本上，Dog应该是一个属性为name的构造函数。在Dog实例创建期间执行时，EventEmitter.call(this)将从EventEmitter构造函数声明的属性追加到Dog。

记住：构造函数仍然是函数，仍然可以用作函数。

//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 

Answer 2

EventEmitter.call(this); 

这条线是大致相当于调用语言超（）与 经典的继承。