How to Fix EADDRINUSE: Address Already in Use and Cannot Find Module ‘express’ Errors

Introduction

Node.js developers often encounter the errors EADDRINUSE: Address already in use and Cannot find module 'express'. These errors can be frustrating but are usually easy to fix. This guide provides step-by-step solutions to help you resolve them.

What Does “EADDRINUSE: Address Already in Use” Mean?

The EADDRINUSE error occurs when a Node.js application tries to bind to a port that is already in use. This is common when you accidentally run multiple instances of the same application or another process is using the same port.

How to Fix “EADDRINUSE” Error

Here are some simple steps to resolve the issue:

1. Stop the Running Process

Find and stop the process using the port. On Linux or macOS, use this command:

lsof -i :

For example, if your application uses port 3000, run:

lsof -i :3000

Then, kill the process with:

kill -9 

2. Use a Different Port

Change the port your application is using. In your Node.js code, update the port number:

const port = 4000; // Use a different port

Restart your application after making this change.

3. Restart Your System

If you can’t identify the process, restarting your system will free up the port.

What Does “Cannot Find Module ‘express'” Mean?

This error occurs when Node.js cannot locate the express module. It usually happens when you forget to install the module or there is an issue with your project’s node_modules folder.

How to Fix “Cannot Find Module ‘express'”

Follow these steps to resolve the error:

1. Install the Express Module

Run the following command to install Express:

npm install express

This command adds Express to your project’s dependencies.

2. Check Your File Path

Ensure you are in the correct project directory where package.json is located before running the installation command.

cd /path/to/your/project

3. Delete and Reinstall node_modules

If the error persists, try deleting the node_modules folder and reinstalling dependencies:

rm -rf node_modules
npm install

4. Use the Correct Import Statement

Ensure your code imports Express correctly:

const express = require('express');

Example Scenario

Imagine you’re developing an application and encounter these errors:

Example 1: EADDRINUSE Error

Error: listen EADDRINUSE: address already in use :::3000

To fix this, you can either stop the running process on port 3000 or change the application’s port to 4000 as shown above.

Example 2: Cannot Find Module ‘express’

Error: Cannot find module 'express'

Resolve this by running npm install express and ensuring your file path is correct.

Conclusion

Both the EADDRINUSE and Cannot find module 'express' errors are common but simple to resolve. By following the steps outlined in this guide, you can quickly fix these issues and continue working on your Node.js application.