MongoDB duplicate key error Node.js

Why This Happens

In Node.js, you tried to insert a document with a duplicate unique field. 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

await User.create({ email: 'taken@test.com' });

The Fix

try {
  await User.create(data);
} catch (err) {
  if (err.code === 11000)
    res.status(409).json({ error: 'Already exists' });
}

Step-by-Step Fix

1. 1

   Identify the error

   Look at the error message: MongoServerError: E11000 duplicate key. 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.