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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Shipping a breaking change into an existing version without bumping it

// Wrong: mutates the v1 contract in place
app.get('/api/v1/users', (req, res) => {
  res.json({ firstName: user.name }); // old clients expect `name`
});

// Correct: freeze v1, put the change in v2
app.use('/api/v1', v1Router); // untouched, still returns { name }
app.use('/api/v2', v2Router); // returns { firstName }

The Solution //

Renaming or removing a field on /api/v1/users and shipping it as-is silently crashes every mobile client still on v1 — there's no version number to signal the change. Any rename, deletion, or type change to an existing field must go into a new version (v2); the old version's contract has to stay frozen forever.

The Error //

Deleting a deprecated version outright instead of returning 410 Gone

// Wrong: router just vanishes
// app.use('/api/v1', v1Router); <- deleted, now 404

// Correct: leave a deliberate 410 stub
app.use('/api/v1', (req, res) => {
  res.status(410).json({ error: 'API v1 is retired. Please update your app.' });
});

The Solution //

Removing the /api/v1 router entirely means old clients get a generic 404 or connection error with zero explanation, which is indistinguishable from a server outage in their crash logs. Keep a lightweight stub route at the old path that responds 410 Gone with a clear message, so ancient clients can detect it and show a 'please update' screen instead of failing silently.