Express and Web Frameworks

Integrating the Result pattern into route handlers using filtered catching.

Most web frameworks rely on throwing exceptions to signal failures. Often, you only want to catch specific, expected errors like a "Not Found" state, while letting other unexpected critical failures bubble up to a global error handler.

Use the named catch pattern (tuple destructuring) combined with error filtering to only capture the NotFoundError. This keeps your logic focused strictly on expected failure modes.

app.get("/users/:id", async (req, res) => {
  const [error, user] = await catchError(
      userService.findById(req.params.id),
      [NotFoundError]
  );

  if (error) {
      return res.status(404).json({ error: error.message });
  }

  return res.status(200).json(user);

});

By providing an array of error classes as the second argument, you ensure that only those specific types are caught. Any other exception will still be thrown normally.