我的代码中的 javascript 观察者模式帮助

Question

请帮助我没有得到我的代码中的错误。这是关于 js 中的观察者模式。收到错误“未捕获的类型错误：无法读取未定义的属性‘push’”。我认为这个错误是因为当我将它与 new 关键字一起使用时，没有在对象上创建“observers”键。

Js 小提琴： https://jsfiddle.net/2808w5x0/

function Subject(){
    this.observers = [];

  return {
    subscribeObserver:function(observer){
        observers.push(observer);
    },
    getObservers:function(){return this.observers;},
    unSubscribeObserver:function(observer){
        var index = this.observers.indexof(observer);
      if(index > -1){
        this.observers.splice(index,1);
      }
    },
    notifyObserver:function(observer){
        var index = this.observers.indexof(observer);
      if(index > -1){
        this.observer[index].notify(index);
      }
    },
    notifyAllObserver:function(){
        this.observers.foreach(function(val,idx){
        val.notify(idx);
      });
    }
  };
}

function Observer(){
    return{
    notify:function(idx){
        console.log("Observer " + idx + " notified.");
    }
  }
}

var subject = new Subject();
console.log("subject ",subject.getObservers());
var ob1 = new Observer();
var ob2 = new Observer();
var ob3 = new Observer();
var ob4 = new Observer();

subject.subscribeObserver(ob1);
subject.subscribeObserver(ob2);
subject.subscribeObserver(ob3);
subject.subscribeObserver(ob4);

subject.notifyAllObserver();

Answer 1

小心，当创建一个新对象new Subject() 时，有一个隐含的return 提供您的新对象。你不需要像以前那样返回你的对象。

---

现在，对于方法，您需要将它们附加到对象的原型。这样，当创建对象时，它会附加这些方法。例如：

function MySuperObject( value ) {
    this.property = value;
};

MySuperObject.prototype.attachedMethod = function() {
    console.log("Property is equal to : " + this.property) + ".";
};

// The object is implicitly returned and stored in <myobj>.
var myobj = new MySuperObject(0);

// Result : Property is equal to : 0.
myobj.attachedMethod();

---

所以，你的代码必须写成：

function Subject(){
  this.observers = [];
}

Subject.prototype.subscribeObserver = function( observer ) {
  this.observers.push(observer);
};

Subject.prototype.getObservers = function() {
  return "There are " + this.observers.length + " observers.";
};

function Observer(){
  // ...
}

var subject = new Subject();
console.log("subject ",subject.getObservers());

var ob1 = new Observer();
var ob2 = new Observer();
var ob3 = new Observer();
var ob4 = new Observer();
subject.subscribeObserver(ob1);
subject.subscribeObserver(ob2);
subject.subscribeObserver(ob3);
subject.subscribeObserver(ob4);

// Or you could simply do :
// for(var i=0; i<4; i++) {
//     subject.subscribeObserver(new Observer());
// }

console.log("subject ",subject.getObservers());

希望对你有帮助！