应用函数-this-slice-函数的call,apply:将非数组变为数组

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<script>

    class Arrays{

           constructor(){

           }

           slice(start,end){

            //    console.log(this);

              if(start<0) start=this.length+start;

              if(end<0) end=this.length+end;

              if(start===undefined) start=0;

              if(end===undefined) end=this.length;

              var a=[];

                for(var i=start;i<end;i++){

                    a.push(this[i]);

                }

                return a;

           }

       }

  

       var divs=document.getElementsByTagName("div");

       arr=[].slice.call(divs);

       console.log(arr);

    

</script>