Incorrect sequence of middlewares when importing a router from another module

[Lezvix]

When an error occurs in a router handler that was declared in another module, the first error handler is triggered, not the one following the path declaration

How to reproduce:

// index.js
const express = require("ultimate-express");
const router = require('./router');

const app = express();
app.use(express.json());
app.set("catch async errors", true);

app.use(function jsonErrorHandler(err, req, res, next){
    if(err){
        return res.send("JSON error");
    }
    next();
})

app.use("/route", router);
app.use(function errorHandler(err, req, res, next) {
    if(err){
        return res.json(err.toString());
    }
    next();
});

app.listen(3000);

// router.js
const express = require("ultimate-express");

const router = express.Router();

router.post("/path", function handler(req, res) {
    throw new Error("Whoops");
    //return res.send("test");
});

module.exports = router;

Expected: Whoops
Actual: JSON error

In Express the sequence is correct, if you move the router to index.js the sequence is also correct

I also encountered that when an error occurred in the handler, the application returned a 404 error and ignored the error interceptor, but I can't reproduce this behavior right now

[nigrosimone]

I tried to fix it without success, I'm just sharing a simplified snippet to reproduce the problem for anyone who wants to try.

const express = require("express");

const router = express.Router();

router.post("/path", function handler(req, res) {
    throw new Error("Whoops");
});

const app = express();
app.use(express.json());
app.set("catch async errors", true);

app.use(function jsonErrorHandler(err, req, res, next){
    if(err){
        return res.send("JSON error");
    }
    next();
})

app.use("/route", router);

app.use(function errorHandler(err, req, res, next) {
    if(err){
        return res.json(err.toString());
    }
    next();
});

app.listen(13333, async() => {
    console.log('Server is running on port 13333');

    const response = await fetch('http://localhost:13333/route/path', { method: 'POST' });
    const body = await response.text();
    console.log(response.status, body);
    process.exit(0);
});

[Lezvix]

I tried reproducing the bug again, but now I can’t reproduce it anymore. The server response matches the expected output and is consistent with what Express returns. Your example has always worked for me without triggering the bug — the issue only appeared when the Router was imported from a different file. Looks like this might be some kind of flaky bug.

[nigrosimone]

This is really weird... I'm on Windows with Node v22.13.0 In my case the bug is always reproducible

[louwers]

I also noticed passing multiple handlers does not work.