How to Solve 'Uncaught ReferenceError: Process is Not Defined' in React

This article explains the “Uncaught ReferenceError: process is not defined” error in React. It explores why this issue appears when using tools like Vite, Webpack, or Create React App with process.env variables.  

Why does your React app suddenly break with the message: "Uncaught ReferenceError: process is not defined"?

This error occurs often than expected, especially when your code relies on process.env inside tools like Vite, Webpack, or Create React App. Knowing whether you're running in a server or client environment makes all the difference.

So what triggers this issue, and how do you fix it without breaking your setup?

Let's find out what causes the 'uncaught reference error process is not defined' React issue, and how to solve it step by step across different React tools.

Key Takeaways

• process is a Node.js object, not available in the browser.

• Using process.env in the client side causes a ReferenceError because process is not defined.

• Resolve this by updating configs or polyfilling process in Webpack/Vite.

• Use .env file and import dotenv properly in React projects.

• Avoid relying on the process directly in browser-executed JavaScript code.

How to fix uncaught ReferenceError process is not defined?

The "uncaught ReferenceError process is not defined react" typically appears when your client-side React application tries to access process.env, a pattern valid in Node.js but not in browsers.

Why does it happen?

• process is a Node.js global object.

• Browsers don’t understand it, which causes the error message.

• This happens when you use process.env or a dependency does.

✅ Solutions by Project Setup

1. Create React App (CRA)

Upgrade to react-scripts@5+:

1npm i react-scripts@latest

If upgrading is not feasible:

• Downgrade to react-scripts@4.0.3

• Lock react-error-overlay to version 6.0.9

In package.json:

1"resolutions": {
2  "react-error-overlay": "6.0.9"
3}

Then:

1rm -rf node_modules
2npm install
3npm start

This resolves the ReferenceError process that occurs on hot reload.

2. Webpack Config

Add polyfill using ProvidePlugin:

1npm install -D process

1const webpack = require('webpack');
2
3module.exports = {
4  plugins: [
5    new webpack.ProvidePlugin({
6      process: 'process/browser',
7    }),
8    new webpack.EnvironmentPlugin(['NODE_ENV']),
9  ],
10};

This ensures you can safely access process.env even on the client side.

3. Vite Config

Modify vite.config.js:

1import { defineConfig, loadEnv } from 'vite';
2import react from '@vitejs/plugin-react';
3
4export default defineConfig(({ mode }) => {
5  const env = loadEnv(mode, process.cwd(), '');
6  return {
7    define: {
8      'process.env': env,
9    },
10    plugins: [react()],
11  };
12});

This makes environment variables available and defined at build time.

4. Quick Client-Side Patch

If configuration is not an option, apply a runtime patch:

1if (!window.process) window.process = {};

Place this at the top of your entry file (index.js or App.js). It prevents the app from crashing due to the ReferenceError process.

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How to use .env file in ReactJS?

Using an .env file allows you to manage environment variables outside your codebase. In React, it’s essential to prefix them correctly.

Steps:

1. Create .env in your project root:

REACT_APP_API_URL=https://api.example.com

1. Access in React:

1const apiUrl = process.env.REACT_APP_API_URL;

1. Restart the server:

1npm start

Note: React only exposes variables prefixed with REACT_APP_.

How to import a variable from a .env file?

You don’t "import" the .env file directly. Instead, you access process.env.VARIABLE_NAME after setting it correctly.

Example:

REACT_APP_TITLE=My React App

Then in your component:

1const title = process.env.REACT_APP_TITLE;

To ensure it works:

• Confirm .env is at project root.

• Restart the server after changes.

• Avoid using process.env directly on the client side without validation.

Choosing the Right Fix

Context	Recommended Fix
CRA with react-scripts ≥ 5	Upgrade and avoid hot reload issues
CRA with older setup	Downgrade + lock react-error-overlay version
Webpack users	Use ProvidePlugin, EnvironmentPlugin, and import dotenv correctly
Vite users	Use loadEnv and define process.env manually
Temporary client-side fix	Use `window.process = window.process

Diagram: Error Context

Fix the Error Now—Before It Breaks Your Build

The "uncaught reference error process is not defined react" usually means a mismatch between your environment setup and how your code runs in the browser. This often happens when process.env is used without proper configuration in tools like Vite or Webpack.

To avoid such errors, always review how your project handles environment variables. Apply fixes that match your setup and test before deploying. Fixing these issues early keeps your React app stable and prevents crashes in production.