javascript 观察者模式对我的代码有帮助

Question

请帮助我没有发现我的代码有什么错误。这是关于js中的观察者模式。获取错误 "Uncaught TypeError: Cannot read property 'push' of undefined"。我认为此错误是因为当我将它与 new 关键字一起使用时，未在对象上创建 "observers" 键。

Js Fiddle: 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

请注意，在创建新对象时 new Subject() 有一个隐含的 return 提供您的新对象。您不需要像以前那样 return 您的对象。

现在，对于这些方法，您需要将它们附加到对象的原型。这样，当创建对象时，它会附加那些方法。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();

因此，您的代码必须写成：

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());

希望对您有所帮助！

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