code: function findAll(predicate) {
          var key,
              elem,
              result = [];
          for (key in _idMap) {
              if (_idMap.hasOwnProperty(key)) {
                  elem = _idMap[key];
                  if (predicate(elem)) {
                      result.push(elem);
                  }
              }
          }
          return result;
      }
docs: Find all elements satisfying the predicate.
  @param {function(Element):boolean} predicate A function to filter elements.
  @return {Array.<Element>} All matched elements.