Question

我看到了这段代码示例：

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

它从EventEmitter'继承'，但call（）方法实际上做了什么？

Answer 1

基本上，Dog应该是具有属性name的构造函数。 EventEmitter.call(this)在Dog实例创建期间执行时，会将EventEmitter构造函数声明的属性追加到Dog。

请记住：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);

这一行大致相当于用语言调用super（）经典继承。

EventEmitter.call（）做什么？

2 个答案: