Passing Variables to the Next Middleware Using Next() in Express.Js

Passing variables to the next middleware using next() in Express.js

Attach your variable to the res.locals object, not req.

Instead of

req.somevariable = variable1;

Have:

res.locals.somevariable = variable1;

As others have pointed out, res.locals is the recommended way of passing data through middleware.

passing variable to next middleware in req in express.js

That's because the User.findOne function is asynchronous. The result of that function is only known in the then block.

const middleware = (req, res, next) => {
    User.findOne({ _id: someId })
        .then(user => {
            req.user = user;
        })
        .catch(err => { });
    next(); // If you put next() here, the request will go straight to the next middleware without waiting for User.findOne() to complete.
};

const middleware = (req, res, next) => {
    User.findOne({ _id: someId })
        .then(user => {
            req.user = user;
            next(); // Putting next() here is correct
        })
        .catch(err => {
            next(err); // Remember to handle error to avoid hanging the request
        });
};

How to pass a parameter to middleware function in Express JS?

I had the same requirement and this approach works for me.

Middleware file validate.js

exports.grantAccess = function(action, resource){
    return async (req, res, next) => {
        try {
            const permission = roles.can(req.user.role)[action](resource);
            // Do something
            next();
        }
        catch (error) {
            next(error)
        }
    }
}

Use of middleware in route file. grantAccess('readAny', 'user')

router.get("/",grantAccess('readAny', 'user'), async (req,res)=>{
    // Do something     
});

Can I send data via express next() function?

In this case you have a few options (only use one of these!):

1. You can just access the req.session.user.username variable from your my_tasks route
2. You can use res.locals
3. You can add data to the req object

In your exports.privateContent function, once a user is found in the database, you can simply add that data to the res.locals:

User.findOne( { 'username': username }, function ( err, obj ) {
  if ( true ) {
    // this variable will be available directly by the view
    res.locals.user = obj;

    // this will be added to the request object
    req.user = obj;

    next();
  } else {
    res.redirect('/');
  }
});

Then in your exports.my_tasks route, res.locals.user will be whatever obj was in the middleware. You can then simply access that in the view as the variable user.

So, all together, you can access the data in your route in these ways:

exports.my_tasks = function ( req, res ) {
   res.render('tasks/tasks', {
     userFromReq: req.user, // this exists because you added in the middleware
     userFromSession: req.session.user, // this was already in the session, so you can access
     userFromRes: [DO NOT NEED TO DO THIS] // because res.locals are sent straight to the view (Jade).
   });
};

Node.js Express How to pass data between middleware?

Demonstrator.find is an asynchronous function, so you should call next in its callback like this

exports.list_all_Demonstrator = function(req, res,next) {
//console.log(req.body)
Demonstrator.find({},  function(err, demo) {
    if (err){
        console.log(err);
    }
    else {
        res.locals.myvar = demo;    
    }
    next(); // <------------
});

};

exports.doSomeStuff = function(req,res,next) {
    var data;
    data = res.locals.myvar
    console.log("Dies ist 2te Funktion:", data);
    res.send(data);
}

Otherwise next will be called before you assign demo to res.locals.myvar

Express: 4.17: Passing the variable to the next function returns undefined (middleware)

Index file and your controller appear fine once working on your route file.

router.route("/getuser", verifyJWT).get((req, res) => {

    console.log(req.app.locals.userId) // <--- Returns undefined

});

Instead of this try to get req...

  router.get("/getuser", verifyJWT, (req, res, next) => {
     console.log(req.app.locals.userId);
     });

How to pass data to next middleware function in NodeJS

Change the route function inside Router class as following and the result of socket.write(1) will be 4:

class Router {
    constructor() {
        this.middleware = new Middleware
    }
    route(data) {
        each(this.middleware.handlers, function (handler) {
            data = handler(data)
        })
        return data
    }
}

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