code: function (h, c) {
          var len = c.length;
          var i = len;
          var f = function () {
              if (!(--i)) h();
          };
          for (var j = 0; j < len; j++) {
              if (c[j].state === 0) {
                  throw Error('Can only use join with sticky channels.');
              }
              c[j].subscribe(f);
          }
          if (!len) h();
      }
docs: Calls the provided function only after all of the channels specified
  have been fired. All channels must be sticky channels.