用JS编写一个函数,返回数组中重复出现过的元素(实例)

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"]