index.js

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

// error handlers
app.use((err, req, res) => {
  console.log('ERROR PASSING THROUGH', err.message);
  // get the error stack
  const stack = err.stack.split(/\n/)
    .map(error => error.replace(/\s{2,}/g, ' ').trim());

  // send out the error as json
  res.status(err.status || 500).json({
    api: err,
    url: req.originalUrl,
    error: err.message,
    stack,
  });
});