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Fix Dotenv Error in Create React App with Webpack Polyfills Guide

Asim Sikka
Fix Dotenv Error in Create React App with Webpack Polyfills Guide

I’m facing an issue with my React app where I keep getting errors related to missing modules in dotenv while using create-react-app. Every time I try to compile, I see errors like “Can’t resolve ‘fs’,” “Can’t resolve ‘path’,” and “Can’t resolve ‘os’.” It turns out that Webpack 5 no longer includes polyfills for Node.js core modules by default, so now I need to configure polyfills manually. Following the provided instructions, I added a webpack.config.js file and tried adding a fallback for the missing modules, like "path": require.resolve("path-browserify"). However, even with these adjustments, the errors persist, and I’m trying to figure out the right configuration to get this working smoothly.

Error Code:

codeCompiled with problems: X

ERROR in ./node_modules/dotenv/lib/main.js 1:11-24

Module not found: Error: Can't resolve 'fs' in 'C:\Users\USER\Desktop\dapps\nefty\node_modules\dotenv\lib'


ERROR in ./node_modules/dotenv/lib/main.js 3:13-28

Module not found: Error: Can't resolve 'path' in 'C:\Users\USER\Desktop\dapps\nefty\node_modules\dotenv\lib'

BREAKING CHANGE: webpack < 5 used to include polyfills for node.js core modules by default.
This is no longer the case. Verify if you need this module and configure a polyfill for it.

If you want to include a polyfill, you need to:
- add a fallback 'resolve.fallback: { "path": require.resolve("path-browserify") }'
    - install 'path-browserify'
If you don't want to include a polyfill, you can use an empty module like this:
resolve.fallback: { "path": false }


ERROR in ./node_modules/dotenv/lib/main.js 5:11-24

Module not found: Error: Can't resolve 'os' in 'C:\Users\USER\Desktop\dapps\nefty\node_modules\dotenv\lib'

BREAKING CHANGE: webpack < 5 used to include polyfills for node.js core modules by default.
This is no longer the case. Verify if you need this module and configure a polyfill for it.

If you want to include a polyfill, you need to:
- add a fallback 'resolve.fallback: { "os": require.resolve("os-browserify/browser") }'
    - install 'os-browserify'
If you don't want to include a polyfill, you can use an empty module like this:
resolve.fallback: { "os": false }

Afterward, I created webpack.config.js and added the fallback as shown below:

codemodule.exports = {
    resolve: {
        fallback: { "path": require.resolve("path-browserify") },
    },
};

There’s still no difference after applying the changes. I checked a similar issue on their GitHub page, but couldn’t find a working fix. Most of the comments just highlighted the problem without offering any practical solutions.

The errors you’re encountering stem from Webpack 5 no longer providing polyfills for certain Node.js core modules (fs, path, and os) by default. This is why dotenv, which relies on these modules, throws errors when used with Webpack 5 in a React app. To resolve this, you need to install the necessary polyfill packages and add appropriate fallbacks in your webpack.config.js file.

Solution:

Install the polyfills for the missing modules:

codenpm install path-browserify os-browserify browserify-fs

Create or modify webpack.config.js to include fallbacks for fs, path, and os as shown below:

codeconst path = require('path');

module.exports = {
    resolve: {
        fallback: {
            "fs": require.resolve("browserify-fs"),
            "path": require.resolve("path-browserify"),
            "os": require.resolve("os-browserify/browser")
        }
    }
};

Ensure your configuration is used by create-react-app: Since create-react-app doesn’t allow custom Webpack configurations directly, you’ll need to use a tool like react-app-rewired to apply your configuration.

codenpm install react-app-rewired --save-dev
code"scripts": {
    "start": "react-app-rewired start",
    "build": "react-app-rewired build",
    "test": "react-app-rewired test"
}
const path = require('path');

module.exports = function override(config) {
    config.resolve.fallback = {
        "fs": require.resolve("browserify-fs"),
        "path": require.resolve("path-browserify"),
        "os": require.resolve("os-browserify/browser")
    };
    return config;
};

Explanation:

  1. Polyfills: Installing path-browserify, os-browserify, and browserify-fs provides browser-compatible versions of the path, os, and fs modules. These modules allow your app to handle dotenv functionality in a way compatible with Webpack 5’s new configuration.
  2. Fallback Configuration: By specifying fallbacks for fs, path, and os, you tell Webpack to use these browser-compatible modules instead of the Node.js versions. This is necessary since React applications run in the browser, which doesn’t have access to native Node.js modules.
  3. Using react-app-rewired: Since create-react-app doesn’t support custom Webpack configurations out of the box, react-app-rewired is a tool that enables you to override and modify the Webpack configuration without ejecting from create-react-app.

By following these steps, your application should compile successfully without throwing module resolution errors for dotenv.

Final Thought:

In handling polyfills in Webpack 5 can be tricky, especially when working with modules like dotenv that rely on Node.js core functionalities. By setting up polyfills for fs, path, and os and using react-app-rewired to customize your configuration, you can smoothly run your React app without hitting these compatibility issues. This solution provides a robust way to bridge the gap between Node.js modules and browser-based environments, ensuring your app remains stable and functional.

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