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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Choosing Node.js for a CPU-heavy workload (image processing, video transcoding) without Worker Threads

// Wrong: blocks the entire server for every user
app.post('/resize', (req, res) => {
  const resized = heavySyncImageResize(req.body.image); // freezes everyone
  res.send(resized);
});

// Correct: offload to a worker thread
const { Worker } = require('worker_threads');
new Worker('./resize-worker.js', { workerData: req.body.image });

The Solution //

Node's single-thread model is built for I/O-bound concurrency, not raw computation. A heavy synchronous task run directly on the main thread — resizing images, transcoding video, running a big regex over huge text — blocks every other concurrent request until it finishes. Either move genuinely CPU-bound work to worker_threads, or reconsider whether Node is the right tool for that specific workload.

The Error //

Installing every package globally (-g) instead of as a local project dependency

# Wrong: not tracked in this project at all
npm install -g express

# Correct: recorded in package.json, reproducible on any machine
npm install express

The Solution //

Beginners often run `npm install -g express` so it 'just works' from anywhere, but this means the project has no record of which packages or versions it actually depends on — package.json stays empty, and the project breaks the moment it's cloned onto another machine. Install project dependencies locally (the default, no -g flag) so they're tracked in package.json and package-lock.json; reserve global installs for CLI tools you use across many unrelated projects (like nodemon or a scaffolding tool).