用JS编写一个函数,返回数组中重复出现过的元素

var arr = [1, 2, 3, 1, 2, 3, 4, 5];
  var getRepeat = function (arr) {
    var obj = {};
    for (var i = 0, len = arr.length; i < len; i++) {
      if (obj[arr[i]] == undefined) {
        obj[arr[i]] = 1;
      } else {
        obj[arr[i]]++;
      }
    }
    for (var key in obj) {
      obj[key] <= 1 && delete obj[key];
    }
    return Object.keys(obj);
  }
  console.log(getRepeat(arr));//打印结果(3) ["1", "2", "3"]