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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Importing a third-party SDK (SendGrid, Stripe, AWS) directly inside controllers across the codebase

// Wrong: vendor lock-in spread across every controller
const sendgrid = require('@sendgrid/mail');
sendgrid.send({ to, subject, text }); // repeated in 30 files

// Correct: one wrapper, everyone else depends on the interface
const { sendEmail } = require('../services/email');
await sendEmail({ to, subject, text });

The Solution //

When 30 different controllers each `require('sendgrid')` directly, switching providers later means hunting down and rewriting every single call site, and any provider-specific error handling gets duplicated everywhere. Wrap the vendor SDK behind a single internal service module (e.g. services/email.js) that controllers call instead — swapping providers becomes a one-file change.

The Error //

Doing request validation with scattered if-statements inside controllers instead of a dedicated validation layer

// Wrong: ad-hoc validation duplicated in every route
router.post('/users', (req, res) => {
  if (!req.body.email || !req.body.email.includes('@')) {
    return res.status(400).json({ error: 'Invalid email' });
  }
  // ...
});

// Correct: schema-driven validation middleware, reused everywhere
const schema = z.object({ email: z.string().email() });
router.post('/users', validate(schema), createUserController);

The Solution //

Manually checking `if (!req.body.email) return res.status(400)...` inline in every route handler mixes validation logic with business logic, makes rules impossible to reuse, and is easy to forget on new endpoints. Centralize validation with a schema library (Zod, Joi) applied as middleware before the controller ever runs, so the controller can assume its input is already trustworthy.