JS内置对象-Array之indexOf和lastIndexOf

indexOf()

 var num = [1, 7, 2, 3, 4, 7, 9]
 var pos = num.indexOf(7)
 var pos1 = num.indexOf(7, 2)
 console.log(pos); // => 1
 console.log(pos1); // => 5

 //封装一个方法实现indexOf的功能
 function ArrayIndexOF(arr, value) {
   //检测value在arr中出现的位置
   for(var i = 0; i < arr.length; i++) {
     if(arr[i] === value) {
       return i;
     }
   }
   return -1;
 }

 console.log(ArrayIndexOF(num, 7)); // => 1

lastIndexOf()

 var num = [1, 7, 2, 3, 4, 7, 9]
 var pos = num.lastIndexOf(7)
 var pos1 = num.lastIndexOf(7,2)
 console.log(pos); // => 5
 console.log(pos1); // => 1