数组去重(indexOf)

 var arr=[1,2,2,3,5,6,7,5,5,4,6];   
      var arr1=[];
      for(var i = 0; i < arr.length; i++){
          if (arr1.indexOf(arr[i]) == -1){
          arr1.push(arr[i])};
        }
      console.log(arr1,'arr1'); //1,2,3,5,6,7,4

array.indexOf()        :查找数组中的 "某个" 元素

let fruits = ["Banana", "Orange", "Apple", "Mango"];
let a = fruits.indexOf("Apple");
console.log(a);    //返回值为2    如果查找数据不存在，返回数据均为-1
let b = fruits.insexOf('aaaaa')
console.log(b);    //返回为-1