请帮助我在代码中没有弄错。这是关于js中的观察者模式。获取错误“Uncaught TypeError: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“观察者”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();
答案 0 :(得分:1)
注意,在创建新对象new Subject()
时,会有一个隐式return
来提供新对象。你不需要像往常一样返回你的对象。
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,将附加那些方法。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();
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());
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希望它有所帮助!