code: function forwardEvent(event, source, target) {
    function forward() {
      var listeners = target.listeners(event);
  
      var n = listeners.length;
  
      // Special case for `error` event with no listeners.
      if (n === 0 && event === 'error') {
        var args = [event];
        args.push.apply(args, arguments);
  
        target.emit.apply(target, args);
        return;
      }
  
      for (var i = 0; i < n; ++i) {
        listeners[i].apply(source, arguments);
      }
    }
  
    source.on(event, forward);
  
    // A reference to the function is necessary to be able to stop
    // forwarding.
    return forward;
  }
docs: Forward events `event` on `source` to all listeners on `target`.  Note: The calling context is `source`.