javascript get unique items of array

1function toUniqueArray(a){
2    var newArr = [];
3    for (var i = 0; i < a.length; i++) {
4        if (newArr.indexOf(a[i]) === -1) {
5            newArr.push(a[i]);
6        }
7    }
8  return newArr;
9}
10var colors = ["red","red","green","green","green"];
11var colorsUnique=toUniqueArray(colors); // ["red","green"]