Consider adding a listen callback and/or using an environment variable for the port so the startup is observable and configurable. For example, you could use const PORT = process.env.PORT || 5701; createServer().listen(PORT, () => console.log(Server listening on ${PORT})); — this is optional but helpful for debugging and deployments.

POST route mismatch with the form in index.html. The server expects POST to /add-expense but src/index.html posts to /submit-expense. Update either the form action or this route so they match; otherwise form submissions will not be handled.

The code uses JSON.parse on the request body. Browser form submissions (without JS) use application/x-www-form-urlencoded or multipart/form-data, not JSON; JSON.parse will throw for typical form payloads. Either change the client to send JSON, or (preferably) parse urlencoded bodies (e.g., use Object.fromEntries(new URLSearchParams(raw))) after checking req.headers['content-type']. This change is required so POST handling works with the provided index.html.

There is no Content-Type inspection before parsing the body. Inspect req.headers['content-type'] and branch parsing logic: JSON.parse only for application/json; use URLSearchParams or querystring.parse for application/x-www-form-urlencoded; do not attempt to parse multipart/form-data unless you implement a parser or remove the enctype on the form. This will make parsing robust.

The code sets const file = path.resolve('db', 'expense.json') but never ensures the db directory exists. If db is missing, create it first (e.g., fs.mkdirSync(path.dirname(file), { recursive: true }) or the async equivalent) before creating a write stream. Without this, writing will fail on a fresh repo.

Error branches currently respond with text/plain (e.g., parse error, missing fields, internal server error). Per checklist, return HTML error pages for validation and save failures so the client receives readable messages in the browser. Keep appropriate status codes, but use Content-Type: text/html and a minimal HTML body.

Form action and enctype are incorrect for the current server. The form posts to /submit-expense and uses enctype="multipart/form-data", but the server expects POST to /add-expense and does not parse multipart form data. Update the form action to match the server route (or change the server route to /submit-expense) and remove the enctype unless you implement multipart parsing on the server. This mismatch will prevent form submissions from being handled.

Method is correct (POST). Keep method="POST" on the form — that is required. Ensure the server route and body parsing are aligned so the POST actually reaches a handler.

Inputs have the correct name attributes: name="date", name="title", and name="amount". This matches the fields the server should extract. Good. Note: client-side required attributes help UX, but server-side validation of date parseability and numeric amount is still necessary.

type="date" and type="number" are helpful for client-side validation, but ensure the server validates these values too (e.g., check !isNaN(new Date(date).getTime()) for date and !Number.isNaN(parseFloat(amount)) for amount) before saving to db/expense.json. The task requires server-side validation.

Consider using an environment-configurable port and a listen callback for clarity. For example, use const port = process.env.PORT || 5701 and createServer().listen(port, () => console.log(Listening on ${port})) so the port can be overridden during testing/deployment and you get a startup log.

The GET handler creates a read stream for index.html and pipes it to the response but does not set the Content-Type header nor an explicit 200 status. Requirement 2.4 requires setting text/html for the form page. Also add an error listener on the read stream to handle missing/unreadable index.html and return a friendly HTML error page.

Consider adding before piping:

res.statusCode = 200;
res.setHeader('Content-Type', 'text/html; charset=utf-8');
form.on('error', (err) => {
  console.error('Read stream error:', err);
  if (!res.headersSent) {
    res.statusCode = 500;
    res.setHeader('Content-Type', 'text/html; charset=utf-8');
    res.end('<!doctype html><html><head><meta charset="utf-8"><title>Error</title></head><body><h1>Server Error</h1><p>Unable to load the form.</p></body></html>');
  } else {
    res.destroy();
  }
});

Then `form.pipe(res);` as you have.

This addresses the missing Content-Type for the form page and handles read errors gracefully.

The GET branch returns a 404 with Content-Type 'text/plain' for unknown URLs. It's not required to change this, but for consistency you may want to return an HTML 404 page (text/html; charset=utf-8) so browser users see a friendly page. If you keep it as plain text that's acceptable for the task, but ensure the form page itself is served with text/html.

The writer error handler sets headers and ends the response on write-stream errors. If the response has already begun, setting headers will throw. Consider checking if (!res.headersSent) before setting headers and ending the response, or otherwise handling the case where headers are already sent (for example, destroy the connection). This prevents potential crashes or unhandled exceptions when write errors occur after response start.

server.on('error', () => {}) currently swallows server-level errors. At minimum log the error so issues are visible during development (and optionally handle fatal errors). For example:

server.on('error', (err) => {
  console.error('Server error:', err);
});

This will help debugging if the server fails to bind to a port or encounters other system-level errors.

Consider making the port configurable and adding a listen callback/logging. For example:

const port = process.env.PORT || 5701;
createServer().listen(port, () => console.log(`Listening on ${port}`));

This is non-blocking — the current hard-coded port works — but it improves flexibility and observability when running in different environments.

Good: the GET handler explicitly sets status 200 and Content-Type to text/html; charset=utf-8, ensuring the form is served as HTML. This resolves the earlier blocker about missing Content-Type and makes the form page consistent for browsers and tests.

The read-stream error handler checks whether headers were already sent, which is good. However, when responding with a 500 it currently calls res.end() with an empty body (lines 33–37). Consider returning a small HTML error page (since GET serves HTML) to make errors clearer to clients and tests. Example: res.end('<!doctype html><html>...<h1>Internal Server Error</h1></html>').

When creating the read stream and piping (createReadStream / form.pipe(res)), the code destroys the read stream when the response closes — good resource handling (lines 28, 43–47).

Path to the data file uses path.resolve('db', 'expense.json'), which matches the requirement to persist to db/expense.json. The directory is created with mkdirSync(path.dirname(file), { recursive: true }) before writing — this satisfies the persistence requirement (lines 63 and 136–137).

Form action and method are correct: action="/add-expense" method="POST", which matches the server POST handler and will send application/x-www-form-urlencoded data that your server parses. Good.

The date input is present with type="date", id="date", name="date", and required. This satisfies the requirement to collect the expense date.

Minor UX suggestion: the label reads Name: but the corresponding input name is title. Consider changing the label to Title: to avoid confusion between field label and internal name. This is not required for functionality but improves clarity.

The amount input uses type="number", step="0.01", id="amount", name="amount", and required — this satisfies the requirement to capture a numeric amount and aligns with server-side parsing/validation.

Optional improvement: the document <title> is currently Document. Consider making it descriptive (e.g., Add Expense) to help users and accessibility tools identify the page purpose.