How to handle errors globally — Intermediate

Server Architecture / Routes Error handling

Use a centralized errorHandler middleware to format errors and set status codes.

Learn: Express recognizes error-handling middleware by its four arguments `(err, req, res, next)`. Log the error, map known status codes, and avoid leaking stack traces in production.

Supplementary examples

Central error handler

function errorHandler(err, req, res, next) {
  const status = err.status || err.statusCode || 500;
  req.log?.error(err);
  res.status(status).json({
    error: err.message || "Internal Server Error",
  });
}

app.use(errorHandler); // after notFound

Course example

const checkForAbbreviationLength = (req, res, next) => {
const abbreviation = req.params.abbreviation;
if (abbreviation.length !== 2) {
next("State abbreviation is invalid.");
} else {
next();
}
};

Additional references & examples

Express.js guide
Routing, middleware order, and request/response lifecycle.
Express error handling
How to define and propagate errors to a central handler.