Express - lesson 5 | HackIndia Skills

Key point

One rule

Your status code should tell the client what happened before they read the JSON.

Use 2xx for success, 4xx when the client sent a bad request, and 5xx when the server failed.

Why it matters

Recruiters will run your API with curl, Postman, or Thunder Client. They should see useful status codes, not only pretty messages.

A frontend also depends on this. If your API returns 200 for an error, the frontend may treat a failed request as a success.

Your to-do

Common choices

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Return 200 when a GET, PUT, or PATCH worked and you are sending data back.
Return 201 when a POST created a new resource, like a student profile or event registration.
Return 400 when required input is missing or invalid.
Return 404 when the requested item or route does not exist.
Return 500 only for unexpected server problems.

0 of 5 done

Example

Use status then json

In Express 5, write the status first, then send JSON. Older tutorials may show removed shortcuts like res.json(obj, status). Do not use those.

app.post('/students', express.json(), (req, res) => {
  const { name, college } = req.body;

  if (!name || !college) {
    return res.status(400).json({
      error: 'name and college are required'
    });
  }

  const student = {
    id: 'stu_101',
    name,
    college
  };

  return res.status(201).json({
    message: 'student created',
    student
  });
});

Example

Not found example

Use 404 when the URL is valid but the resource is missing. For example, the route exists, but that project ID is not in your data.

app.get('/projects/:id', (req, res) => {
  const project = projects.find((item) => item.id === req.params.id);

  if (!project) {
    return res.status(404).json({
      error: 'project not found'
    });
  }

  return res.status(200).json({ project });
});

Common mistake

Avoid fake success

Do not return 200 with { error: 'missing name' }. That makes clients guess what happened.

Also avoid using 500 for validation mistakes. If the user forgot a field, the server did not crash. The client sent a bad request, so use 400.

Tip

Ask AI carefully

If you use ChatGPT, Gemini, or Claude to draft route handlers, ask it to include meaningful HTTP status codes. Then check every response yourself.

Look for old Express patterns. In Express 5, use res.status(status).json(obj) and res.status(status).send(body).

Prompt:
Write an Express 5 route for POST /registrations.
Use express.json(), validate name and email, return 400 for missing fields, 201 for created, and JSON responses.
Do not use old res.json(obj, status) syntax.