编写一个数组去重的方法

<script>
var arr = [1,2,"2","4",5,2,1];

var newArr = removeRepetition(arr);
console.log(newArr);

function removeRepetition(arr){
var newArr = [];
//typeof (arr) == "string"?newArr = "":newArr = [];
if (newArr.length == 0) {
newArr.push(arr[0]);
}
if (newArr.length != 0) {
for (var i in arr) {
if (newArr.indexOf(arr[i]) == -1) {
newArr.push(arr[i]);
}
}
}
if(typeof arr == "object"){
return newArr;
}
if(typeof arr == "string"){
var arrStr = "";
for(var i=0;i<newArr.length;i++){
arrStr += newArr[i];
}
return arrStr;
}
}

</script>