Express: error handled at unknown error handler

Created on 27 Sep 2017 · 2Comments · Source: expressjs/express

express version : 4.15,
node version: 8.1.4

im currently experiencing an odd behavior within my application, I have nested routes and im defining my routes like this

const router = require('express').Router();
const m = require('../modules/index').v1;

router.route('/')
  .post(m.create)
  .get(m.list)
  .all(m.transformer);

router.route('/:id')
  .all(m.middlewareById)
  .put(m.editById)
  .delete(m.deleteById)
  .get(m.getById)
  .all(m.transformer);
module.exports = router;

Im currently developing m.create API controller, and when and error occurs that is not handled sends me a response of HTML page with error object.

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>Error</title>
    </head>
    <body>
        <pre>[object Object]</pre>
    </body>
</html>

I want to eliminate this behavior and response with JSON only, but somehow its by passing my defined request handlers, and instead of getting handled at a middle ware that I specify, or the one at app.js
its is being handled somewhere else mysteriously, i've been express user for 3 or more years and this is the first time im facing such behavior.
has something changed in new Express version?

_app.js_

const express = require('express');
const path = require('path');
// const favicon = require('serve-favicon');
const logger = require('morgan');
const cookieParser = require('cookie-parser');
...

app.use('/', index);
app.use('/systemadmin', systemAdminRoutes);

// catch 404 and forward to error handler
app.use((req, res, next) => {
  const err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handler
app.use((err, req, res) => {
  // next is the last argument in above function
  // set locals, only providing error in development
  // res.locals.message = err.message;
  // res.locals.error = req.app.get('env') === 'development' ? err : {};
  debug(err); // nothing logs here 
  debug(err.message);
  debug(err.name);
  debug(err.errorCode);
  debug(err.stack);
  // render the error page
  res.status(err.status || 500);
  res.send({error: err.message}); //this never gets called
});

module.exports = app;

4.x question

Source