Error Handling

useErrorHandler()

Kaelum provides a global error handler that catches unhandled exceptions across all routes and middleware.

app.useErrorHandler();

With Options

app.useErrorHandler({ exposeStack: false });

How It Works

Captures unhandled exceptions in routes or middleware
Returns JSON for API endpoints (when Accept: application/json)
Returns HTML for web page requests
Must be called after all routes and middleware

Automatic Async Error Catching

Kaelum wraps all route handlers in a try/catch. Async errors (promise rejections) are automatically caught and passed to Express’s next(err):

app.addRoute("/users", {
  get: async (req, res) => {
    const users = await db.getUsers(); // if this throws, it's caught
    res.json(users);
  }
});

No need for manual try/catch in every async handler.

Custom Error Pages

For web apps, you can customize the error response by adding your own error middleware before calling useErrorHandler():

app.use((err, req, res, next) => {
  if (req.accepts("html")) {
    res.status(500).render("error", { message: err.message });
  } else {
    next(err); // fallback to Kaelum's handler
  }
});

app.useErrorHandler();