let observer = {
    /*訂閱功能*/
    addSubscriber: function (cb) {
      this.subscribers.push(cb);
    },
    /*退訂功能*/
    removerSubscriber: function (cb) {
      let index = this.subscribers.indexOf(cb);
      this.subscribers.splice(index, 1)
    },
    // 發(fā)布功能
    publish: function (what) {
      for (let i in this.subscribers) {
        if (typeof this.subscribers[i] == "function") {
          this.subscribers[i](what);
        }
      }
    },
    // 讓每個對象具有訂閱功能
    make:function(obj){
      for(let key in this){
        obj[key] = this[key];
      }
      obj.subscribers = [];
    },
  }

  // 定義對象
    let o = {};
    // 實現(xiàn)數(shù)據(jù)綁定 實現(xiàn)具有發(fā)布訂閱功能
    observer.make(o);
    // 發(fā)布
    $("#num").oninput = function(){
      o.publish(this.value);
    };
    // 平方功能
    o.addSubscriber(function(num){
      $("#sqrnum").value = Math.pow(num,2);
    });
    o.addSubscriber(function(num){
      $("#cubenum").value = Math.pow(num,3);
    });
    o.addSubscriber(function(num){
      $("#fourFangnum").value = Math.pow(num,4);
    });
    o.addSubscriber(function(num){
      $("#sqrtnum").value = Math.sqrt(num);
    });
  }
  function $(str){//#box .cls p
    if(str.charAt(0)=="#"){
      return document.getElementById(str.substring(1));
    }else if(str.charAt(0)=="."){
      return document.getElementsByClassName(str.substring(1));
    }else{
      return document.getElementsByTagName(str);
    }
  }