数组去重

1. indexOf 方法

   // indexOf
   function i(a) {
     var b = []
     for (var i = 0; i < a.length; i++) {
       if (b.indexOf(a[i]) === -1) {
         b.push(a[i])
       }
     }
     return b
   }
   
   var a = [1, 1, 1, 2, 3]
   console.log(i(a))
   

2. Set 方法

   // ES6 Set
   function newArr(arr) {
     return Array.from(new Set(arr))
   }
   
   var arr = [1,2,3,4,2,5,3,7,4,6]
   console.log(newArr(arr))	// [ 1, 2, 3, 4, 5, 7, 6 ]