conditionally use a middleware depending on request parameter express

Question

I am trying to decide on a middleware to use based on request query parameter.

in the main module I have something like this:

app.use(function(req, res){   if (req.query.something) {     // pass req, res to middleware_a   } else {     // pass req, res to middleware_b   } }); 

middleware_a and middleware_b are both express apps themselves created by express() function and not regular middleware functions (function(req, res, next))

can't find a way to do it

Answer 1

There is nothing magical about connect/express 'middleware': they are just functions - and you can call them as you would call any other function.

So in your example:

app.use(function(req, res, next){   if (req.query.something) {     middlewareA(req, res, next);   } else {     middlewareB(req, res, next);   } }); 

That said, there might be more elegant ways of constructing hierarchical express applications. Check out TJ's video

Answer 2

I know this issue is old, but I would like to share my solution. I solved this by making a function that returned a Middleware with a callback.

Example middleware:

function isAdminUser(callback){     return function(req, res, next){         var userId = callback(req);         // do something with the userID         next();     } } 

Then you can do the following in the express router object

app.use(isAdminUser(function(req){     return req.body.userId     });