docs: function filterArray(arr, callback) {
    var len = arr.length;
    var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
    var result = [];
    for (var i = 0; i < len; i++) {
      if (i in arr) {
        var val = arr[i];
        if (callback.call(thisArg, val, i, arr)) {
          result.push(val);
        }
      }
    }
    return result;
  }