next('route') in middleware does not behave as documented when added with app.use

Hello,

I have been able to reduce this issue to a very simple test case:

const express = require('express');
const app = express();

const bypass = (req, res, next) => {
  return next('route');
};

app.use(bypass, (req, res, next) => {
  res.send('Should not happen');
});

app.get('/', (req, res, next) => {
  res.send('Should happen');
});

app.listen(3000);

The first call to app.use defines a middleware chain that should be bypassed by the first middleware, according to the documentation in http://expressjs.com/en/4x/api.html#app.use In this test case, if I replace app.use by app.(all|get|post|...) it behaves as expected.

In my use case, though, I’m mounting a router with some subdomain precondition so I would like to write:

app.use(subdomainPrecondition, require('./subdomainRouter'));

I’m using express 4.14.0 on node 6.9.1.

Regards,

Laurent

[dougwilson]

Ah, thanks for the explanation!

I have found a way to do it, though. I can wrap my router in the subdomain middleware and invoke the router function myself.

Yes, with the design of Express, this is exactly how you’re supposed to do it 😃 You can find this pattern in our own middlewares, for example the vhost middleware (https://expressjs.com/en/resources/middleware/vhost.html), which is doing basically what your little example does.

[LaurentVB]

Ok, I get it. Thanks for your patience 😃

The problem I’m trying to solve is this: a dynamic subdomain per client, which will load the app (think XXX.slack.com loads XXX’s slack). If no such subdomain exists, then fallback on the regular website and following routes.

I have found a way to do it, though. I can wrap my router in the subdomain middleware and invoke the router function myself.

module.exports = (router) => {
  return (req, res, next) => {
    const subdomain = req.subdomains[0];
    if (subdomain) {
      res.locals.subdomain = subdomain;
      router(req, res, next);
    } else {
      next();
    }
  };
};

And I’ll call it this way:

const subdomain = require('./subdomain');
const router = require('./router');
app.use(subdomain(router));

I like it slightly less than app.use(subdomain, router); that I initially though should work, but I can live with it.