document.onclick = function (e) {
      let a = e || window.event;  //處理相容，獲取時間物件
      let o = a['target'] || a['srcElement'];//處理相容，獲取資訊
      console.log(o.tagName)
    }
    //優雅實現
    function EleName(evt){
      evt=evt||window.event;
      let slttag=evt.target||evt.srcElement;
      let elename=slttag&&slttag.tagName?slttag.tagName.toLowerCase():'no tagName';
      console.log(elename);
    }

    window.onload=function(){
      let el =document.querySelector('body');
      el.onclick=EleName;
    }

 // 示例一
    function class1(){
      console.log('初始化')
    }
    class1.prototype.menthod=function(asg){
      console.log(asg)
      return this;
    }
    let cl=new class1();
    cl.menthod('第一次呼叫').menthod('第二次呼叫');
   // 示例二
    let obj={
      a:function(){
        console.log(
 
'a')
        return this;
      },
      b:function(){
        console.log('b');
        return this;
      }
    }
    obj.a().b();
    // 示例三
    class MyMath{
      constructor(value){
        this.hasInit=true;
        this.value=value;
        if(!value){
          this.value=0;
          this.hasInit=false
 
;
        }
      }
      add(){
        let args=[...arguments];
        let initValue=this.hasInit?this.value:args.shift();
        const value=args.reduce((prev,curv)=>prev+curv,initValue);
        return new MyMath(value)
      }
      minus(){
        let args=[...arguments];
        let initValue=this.hasInit?this.value:args.shift();
        const value=args.reduce((prev,curv)=>prev-curv,initValue);
        return new MyMath(value)
      }
    }
    let test=new MyMath();
    let res=test.add(12,32,21).minus(12).add(123);
    console.log(res.value)

    //原型鏈是實現鏈式呼叫
    Number.prototype.add=function(){
      let _that=this;
      _that=[...arguments].reduce((prev,curv)=>prev+curv,_that);
      return _that;
    }
    Number.prototype.minus=function(){
      let _that=this;
      _that=[...arguments].reduce((prev,curv)=>prev-curv,_that);
      return _that;
    }

    let num=0;
    console.log(num.add(1,2,3,4).minus(1,2,2))