express-middleware-errror.js

  app.get("/api/loggedin.json", [

    function(req, res, next) {
      if (!req.user) return next(new Error("not logged in"));
      return next();
    },
    function(req, res, next) {
      return req.json({
        "loggedin": true
      });
    },
    function(err, req, res, next) {
      return req.json({
        "loggedin": false
      });
    },
  ]);