code: function getMimeType(types) {
          if (!types) return MSIE_MIME_TYPE; // IE 9 workaround.
          for (var i = 0; i < types.length; i++) {
            if (types[i] == MSIE_MIME_TYPE || types[i] == EDGE_MIME_TYPE ||
                types[i].substr(0, MIME_TYPE.length) == MIME_TYPE) {
              return types[i];
            }
          }
          return null;
        }
docs: Given the types array from the DataTransfer object, returns the first valid mime type.
  A type is valid if it starts with MIME_TYPE, or it equals MSIE_MIME_TYPE or EDGE_MIME_TYPE.