JavaScript development is a dynamic and often complex endeavor, and errors can sometimes feel like inevitable companions. Among these challenges is the perplexing “Module not found: Error: Can’t resolve ‘core-js/es6’” error. This error typically arises when webpack or a similar module bundler encounters difficulties in locating a required module. In this article, we’ll unravel the common causes of this error and discuss potential solutions. Moreover, we’ll explore an interesting scenario where a ‘polyfill.js’ file plays a pivotal role in handling ‘core-js’ in your project.

Demystifying the ‘Module not found’ Error

The “Module not found” error is a familiar adversary to JavaScript developers. It rears its head when webpack struggles to locate a module that your project depends on. Specifically, the error message “‘Can’t resolve ‘core-js/es6’” suggests that webpack is searching for the ‘core-js/es6’ module and encountering difficulties.

Common Causes of the Error:

  1. Missing Dependencies: The ‘core-js’ dependency might be absent from your project.

  2. Webpack Configuration Issues: Your webpack configuration may require adjustments to handle the ‘core-js’ module correctly.

  3. Webpack Aliasing Problems: Configuration settings, like aliases in webpack, could interfere with module resolution.

Now, let’s explore the steps to resolve this error.

Resolving the ‘Module not found’ Error

1. Install or Update ‘core-js’

The most common cause of this error is the absence of the ‘core-js’ package in your project’s dependencies. To resolve this, install ‘core-js’ by running:

npm install core-js

Or with yarn:

yarn add core-js

If you already have ‘core-js’ installed, ensure that it’s up to date by updating it:

npm update core-js

2. Check Your Webpack Configuration

Review your webpack configuration to ensure it’s correctly set up to resolve ‘core-js’ and other dependencies. Verify that there are no aliases or module resolution settings that might be affecting the resolution of ‘core-js’.

3. Clear Node Modules and Reinstall

Sometimes, issues with the node_modules cache can cause module resolution problems. To resolve this, clear the node_modules cache and reinstall your dependencies:

rm -rf node_modules
npm install

4. Verify Import Statements

Check your import statements to ensure that you are importing ‘core-js’ correctly. It should look like this:

import 'core-js/es6';

5. Webpack Loader Configuration

If you are using webpack with loaders like Babel, make sure your loader configuration includes ‘core-js’ in its transpilation process. Ensure that your .babelrc or webpack configuration correctly transpiles ‘core-js’ and your application code.

6. Check Your Project Structure

Ensure that you are running your build or development server from the correct project directory. Sometimes, working in the wrong directory can lead to module resolution issues.

A Unique Solution: ‘polyfill.js’

In some cases, a specific solution involves introducing a ‘polyfill.js’ file into your project’s structure. This ‘polyfill.js’ file can serve as a bridge to handle ‘core-js’ in your project, particularly when dealing with version 3.0 and beyond.

Project Structure:

  ├── src/
  │    ├── polyfill.js
  │    ├── main.scss
  │    └── main.jsx
  ├── webpack.config.js
  └── ...

In ‘polyfill.js’, include the following line:

import 'core-js';

Next, add ‘polyfill.js’ to your webpack entry configuration:

entry: ['./src/main.scss', './src/polyfill.js', './src/main.jsx']

This setup effectively integrates ‘core-js’ into your project, allowing it to polyfill necessary features.

For more information on this approach, you can refer to this GitHub discussion. The library author, zloirock, explains:

“ES6 changes behavior almost all features added in ES5, so core-js/es6 entry point includes almost all of them. Also, as you wrote, it’s required for fixing broken browser implementations.”


The “Module not found: Error: Can’t resolve ‘core-js/es6’” error can be a stumbling block in JavaScript development. By following the steps outlined in this article and considering unique solutions like introducing a ‘polyfill.js’ file, you can effectively diagnose and resolve this error. Ultimately, your project will run smoothly, without interruptions, and you’ll be equipped to handle ‘core-js’ in your JavaScript applications. Plus, using an IDE like Visual Studio Code can further enhance your development experience. Happy coding!