js 数组去重

var arr = [1,2,3,4,2,1,23]
var newArr = [];
var setArr = [];
for(var i=0;i<arr.length;i++){
  if(newArr.indexOf(arr[i]) == -1){
    	newArr.push(arr[i]);
    }else{
    	setArr.push(arr[i]);
    }
}
console.log(newArr) //[1, 2, 3, 4, 23]   去重数组
console.log(setArr) // [2, 1]  //重复数组