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