高效率去掉js数组中重复项

function unique(arr) {
    var result = [], isRepeated;
     for (var i = 0, len = arr.length; i < len; i++) {
         isRepeated = false;
         for (var j = 0, len = result.length; j < len; j++) {
             if (arr[i] == result[j]) {   
                 isRepeated = true;
                break;
             }
         }
         if (!isRepeated) {
             result.push(arr[i]);
         }
     }
     return result;
 }

function unique(arr) {
    var result = [], hash = {};
    for (var i = 0, elem; (elem = arr[i]) != null; i++) {
        if (!hash[elem]) {
            result.push(elem);
            hash[elem] = true;
        }
    }
    return result;
}