Port already in use EADDRINUSE Node.js

Why This Happens

In Node.js, another process is already using the port. This is one of the most common Node.js errors developers encounter. Understanding the root cause helps you fix it quickly and prevent it from recurring.

The Problem

app.listen(3000);

The Fix

// Kill existing process:
// lsof -ti:3000 | xargs kill
app.listen(process.env.PORT || 3000);

Step-by-Step Fix

1. 1

   Identify the error

   Look at the error message: Error: listen EADDRINUSE. This tells you exactly what went wrong.

2. 2

   Find the cause

   Check the stack trace to find which line of your Node.js code triggered this error.

3. 3

   Apply the fix

   Use the corrected code pattern shown above. Test to confirm the error is resolved.