var arr = [1,2,4,5,77,333,451,767] function searching(target){ //声明要使用的变量 var start =0,end =arr.length-1,middle,element; while(start <= end){ //确定中间值索引 middle =Math.floor((start +end)/2); //给中间值赋值 element = arr[middle]; if( element === target){ return middle; }else if(target < element){ end = middle -1; }else if(target > element){ start = middle +1; }else{ return -1; } } }