MODULE_NOT_FOUND Error in JavaScript (Node.js)

The MODULE_NOT_FOUND error is a common error in Node.js that occurs when the runtime fails to locate a required module. This can happen for various reasons, including missing dependencies, incorrect paths, or misconfigured module resolutions.

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Understanding the Error

When you see an error message like:

Error: Cannot find module 'express'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:815:15)
    at Function.Module._load (internal/modules/cjs/loader.js:667:27)
    at Module.require (internal/modules/cjs/loader.js:887:19)
    at require (internal/modules/cjs/helpers.js:74:18)

It indicates that Node.js is unable to find the express module (or any other module that’s missing).

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Common Causes and Fixes

1. Missing Node Modules (Dependencies Not Installed)

If you forgot to install a required package, Node.js won’t be able to find it.

Solution: Install the missing package

Run the following command to install the missing package:

npm install <package-name>

For example, if express is missing:

npm install express

If using yarn:

yarn add express

If using pnpm:

pnpm add express

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2. Wrong Module Name in require or import

Node.js is case-sensitive, so ensure that the module name matches exactly.

Incorrect:

const Express = require('Express'); // Wrong capitalization

Correct:

const express = require('express');

If using ES modules (import syntax):

Incorrect:

import express from "Express";

Correct:

import express from "express";

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3. Dependency Installed Locally Instead of Globally (or Vice Versa)

Sometimes, you install a package globally, but the project expects a local installation.

Solution:

If you installed a package globally, but your script is running in a local context, install it locally:

npm install <package-name>

Alternatively, if you need it globally:

npm install -g <package-name>

Example:

npm install -g nodemon

If running nodemon still gives a MODULE_NOT_FOUND error, try:

npx nodemon server.js

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4. node_modules Folder Missing

If the node_modules folder is missing (e.g., after cloning a repository), dependencies won’t be found.

Solution: Reinstall dependencies

Run:

npm install

Or:

yarn install

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5. Incorrect File Path When Requiring a Local Module

If you are trying to import a local module but provide an incorrect path, the module won’t be found.

Incorrect (missing ./ for a local file):

const myModule = require('myModule'); 

Correct:

const myModule = require('./myModule');

If your file is inside a subfolder:

const myModule = require('./utils/myModule');

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6. Wrong main File in package.json

If you’re working with a custom module, ensure the main entry in package.json correctly points to the main file.

Example package.json:

{
  "name": "myModule",
  "version": "1.0.0",
  "main": "index.js"
}

If index.js doesn’t exist, update the main field to point to the correct file.

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7. Circular Dependencies

If two modules depend on each other, one may not be fully loaded, causing MODULE_NOT_FOUND.

Solution:

Refactor the code to avoid circular dependencies. Consider moving shared logic to a separate module.

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8. Module Installed in Wrong Directory

Check if the package is installed in the correct directory by running:

npm list <package-name>

Example:

npm list express

If it’s not listed, install it again using:

npm install express

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9. Global Packages Not in NODE_PATH

If you installed a package globally but Node.js doesn’t recognize it, ensure NODE_PATH is correctly set.

Solution:

Find the global package location:

npm root -g

Then, add it to NODE_PATH:

export NODE_PATH=$(npm root -g)

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10. Using ES Modules Incorrectly

If you are using ES modules (import instead of require), ensure your package.json contains:

{
  "type": "module"
}

Also, ensure you use the correct file extension:

import express from 'express'; // Use .js extension in imports

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11. Corrupted node_modules or package-lock.json

If all else fails, your node_modules folder or package-lock.json may be corrupted.

Solution:

1. Delete node_modules and package-lock.json: rm -rf node_modules package-lock.json
2. Reinstall dependencies: npm install

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Summary of Fixes

Cause	Solution
Dependency missing	npm install <package>
Wrong module name	Check case sensitivity
Installed globally instead of locally	npm install <package>
node_modules missing	npm install
Wrong file path	Use ./ for local modules
Incorrect main file in package.json	Update main field
Circular dependencies	Refactor code
Installed in wrong directory	Check with npm list <package>
Global packages not found	Update NODE_PATH
ES modules issues	Ensure "type": "module" in package.json
Corrupted node_modules	Delete and reinstall

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By following these steps, you should be able to resolve the MODULE_NOT_FOUND error in Node.js and ensure that your dependencies load correctly.