How to fix Error: Cannot find module 'express' in Node.js

If the error mentions a third-party package (like 'express', 'cors', etc.), install it locally in your project:

npm install express

For multiple packages, install them all at once:

npm install express cors body-parser

Never use the -g (global) flag for project dependencies, as Node.js looks for modules in the local node_modules directory first.

If you've just cloned a repository or the node_modules directory is missing, install all dependencies listed in package.json:

npm install

This command reads package.json and package-lock.json (if present) and installs all required dependencies into the node_modules directory. Make sure you run this command in the project root directory where package.json is located.

If the error is for a local file you created, ensure the path is correct. For CommonJS:

// Wrong - missing './'
const myModule = require('utils/helper');

// Correct - relative path
const myModule = require('./utils/helper');

For ES Modules (when using "type": "module" in package.json), include the file extension:

// Wrong - missing extension
import myModule from './utils/helper';

// Correct - includes .js extension
import myModule from './utils/helper.js';

Paths are case-sensitive on Linux servers, so ensure exact casing matches your file system.

If dependencies are corrupted, do a complete clean reinstall. On macOS/Linux:

rm -rf node_modules
rm -f package-lock.json
npm cache clean --force
npm install

On Windows (Command Prompt):

rd /s /q "node_modules"
del package-lock.json
npm cache clean --force
npm install

This removes all installed packages, clears the npm cache, and reinstalls everything fresh from the registry. Restart your IDE or terminal after this process.

Open your package.json and ensure the module is listed in the correct section:

{
  "dependencies": {
    "express": "^4.18.2"
  },
  "devDependencies": {
    "nodemon": "^3.0.1"
  }
}

Production dependencies (needed to run the app) belong in dependencies. Development tools (testing, building) go in devDependencies. Some deployment platforms prune devDependencies, which can cause MODULE_NOT_FOUND errors in production if packages are misplaced.