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

Question

Well, my question is I want to pass some variable from the first middleware to another middleware, and I tried doing this, but there was "req.somevariable is a given as 'undefined'".

---

//app.js
..
app.get('/someurl/', middleware1, middleware2)
...

---

////middleware1
...
some conditions
...
res.somevariable = variable1;
next();
...

---

////middleware2
...
some conditions
...
variable = req.somevariable;
...

Answer 1

This is what the res.locals object is for. Setting variables directly on the request object is not supported or documented. res.locals is guaranteed to hold state over the life of a request.

res.locals

An object that contains response local variables scoped to the request, and therefore available only to the view(s) rendered during that request / response cycle (if any). Otherwise, this property is identical to app.locals.

This property is useful for exposing request-level information such as the request path name, authenticated user, user settings, and so on.

app.use(function(req, res, next) {
    res.locals.user = req.user;  
    res.locals.authenticated = !req.user.anonymous;
    next();
});

To retrieve the variable in the next middleware:

app.use(function(req, res, next) {
    if (res.locals.authenticated) {
        console.log(res.locals.user.id);
    }
    next();
});