我看到了这个代码示例:
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?
我看到了这个代码示例:
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?
基本上,Dog
应该是具有属性的构造函数name
。在实例创建EventEmitter.call(this)
期间执行时,将从构造函数Dog
声明的属性附加到.EventEmitter
Dog
请记住:构造函数仍然是函数,并且仍然可以用作函数。
//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
EventEmitter.call(this);
这一行大致相当于在具有经典继承的语言中调用 super()。