//let p = Observer.prototype
p.on = function(eventName, fn){
 let listener = this.listener = this.listener || [];
 if(typeof eventName === 'string' && typeof fn === 'function'){
  if(!listener[eventName]){
   listener[eventName] = [fn];
  }else{
   listener[eventName].push(fn);
  }
 } 
}

//let p = Observer.prototype
p.off = function(eventName, fn){
 let listener = this.listener = this.listener || [];
 let actionArray = listener[eventName];
 if(typeof eventName === 'string' && Array.isArray(actionArray)){
  if(typeof fn === 'function'){
   actionArray.forEach( (func, i, arr) => {
    if(func === fn){
     arr.splice(i,1); 
    }
   });
  }
 }
}

//let p = Observer.prototype
p.emit = function(eventName){
 let listener = this.listener = this.listener || [];
 let actionArray = listener[eventName];
 if(Array.isArray(actionArray)){
  actionArray.forEach( func => {
   if(typeof func === 'function'){
    func(); 
   }
  }); 
 }
}

//let p = Observer.prototype
p.observe = function(key, data){
 if(typeof data === 'object'){
  let ob = new Observer(data); 
  //关联父节点
  ob._parent = {
   key,
   ob: this
  };
 } 
}

//let p = Observer.prototype
p.notify = function(eventName){
 let ob = this._parent && this._parent.ob;
 let key = ob && this._parent.key || 'root';
 console.log('parent--'+key+' event--'+eventName);
 this.emit(eventName);
 //判断节点是否有父节点，若有，就向上传递事件
 ob && ob.notify(eventName); 
}