How to return consistent API errors — Intermediate

Misc / Other Coding & architecture practices

Use JSON error objects and appropriate status codes; centralize formatting in error middleware.

Learn: Clients and frontends depend on predictable error JSON. Pick a shape (e.g. { error: string }) and use it for validation, not found, and server errors.

Supplementary examples

errorHandler shape

function errorHandler(err, req, res, next) {
  const status = err.status || 500;
  res.status(status).json({
    error: err.message,
    ...(process.env.NODE_ENV === "development" && { stack: err.stack }),
  });
}

Course example

// Validation
res.status(400).json({ error: "username is required" });

// Not found (in service or controller)
const err = new Error("User not found");
err.status = 404;
throw err;

// errorHandler sends: { error: err.message }

Additional references & examples

Express error handling
Central error middleware and status codes.
HTTP status codes (MDN)
When to use 200, 201, 204, 400, 404, 500, and related codes.