HTML MASTER CLASS /// LEARN TAGS /// BUILD STRUCTURE /// SEMANTIC WEB /// HTML MASTER CLASS /// LEARN TAGS ///

Untitled Lesson

⚡ Total XP: 0|💻 backend XP: 0

Skill Matrix

UNLOCK NODES BY LEARNING NEW TAGS.

Select an unlocked node to view details root

Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Using fs.readFileSync (or any *Sync fs call) inside a request handler

// Wrong: blocks every user's request while this one reads the disk
app.get('/report', (req, res) => {
  const data = fs.readFileSync('./report.csv');
  res.send(data);
});

// Correct
import fs from 'node:fs/promises';
app.get('/report', async (req, res) => {
  const data = await fs.readFile('./report.csv');
  res.send(data);
});

The Solution //

Every *Sync method in the fs module blocks Node's single thread until the operation finishes, freezing the entire server for every concurrent user, not just the one who triggered it. Always use fs/promises (or the callback API) inside anything that runs per-request; reserve *Sync calls for one-time startup code that runs before the server starts accepting connections.

The Error //

Hardcoding OS-specific path separators instead of using the path module

// Wrong: breaks on Linux/macOS deployment
const file = __dirname + '\\views\\index.html';

// Correct: works everywhere
import path from 'node:path';
const file = path.join(__dirname, 'views', 'index.html');

The Solution //

Concatenating strings with a literal backslash (Windows) or forward slash (Linux/macOS) to build file paths works on the developer's machine but breaks the moment the code runs on a different OS — a very common surprise when deploying a Windows-developed app to a Linux container or server. Always build paths with path.join() or path.resolve(), which use the correct separator for whatever OS the code is actually running on.