Uncaught Reference Error: process is not defined (Browser)

Uncaught ReferenceError: process is not defined (Browser)

This error occurs when JavaScript code running in a browser environment tries to access process, which is a global object available in Node.js but not natively in web browsers.

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Understanding the Error

What does the error mean?

The error message:

Uncaught ReferenceError: process is not defined

suggests that the JavaScript code is referencing process, but the browser does not recognize this variable because it is specific to Node.js.

Why does this happen?

1. Using Node.js-specific Code in the Browser
   • Some libraries use process.env to access environment variables.
   • If you try to run a Node.js script in a browser without modifications, this error may occur.
2. Missing Polyfills in Webpack or Vite
   • Webpack 5 and later versions no longer automatically provide polyfills for Node.js core modules.
   • Vite and other modern build tools may also lack built-in support for Node.js globals.
3. Importing Server-Side Code in a Client-Side Context
   • Some modules are intended for server-side execution only and should not be used in the browser.
4. Libraries Assuming a Node.js Environment
   • Some older packages assume the presence of Node.js globals like process.

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Step-by-Step Solutions

Solution 1: Use typeof process !== 'undefined' to Check Availability

Before using process, check if it exists:

if (typeof process !== 'undefined') {
    console.log(process.env);
} else {
    console.log("process is not available in the browser");
}

This prevents the error from occurring when process is unavailable.

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Solution 2: Replace process.env with a Config File

If your code is accessing process.env for environment variables, create a configuration file instead:

const config = {
  API_URL: "https://api.example.com",
  DEBUG_MODE: true
};

Then import it where needed:

import { config } from './config.js';
console.log(config.API_URL);

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Solution 3: Use a Polyfill for process in Webpack

If you’re using Webpack, add a polyfill in webpack.config.js:

module.exports = {
  resolve: {
    fallback: {
      process: require.resolve("process/browser")
    }
  }
};

Then install the process package:

npm install process --save-dev

And import it in your code:

import process from "process";
console.log(process.env);

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Solution 4: Use Vite Define Plugin to Mock process.env

For Vite users, modify vite.config.js:

import { defineConfig } from 'vite';

export default defineConfig({
  define: {
    'process.env': {}
  }
});

This ensures that process.env is defined as an empty object instead of causing an error.

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Solution 5: Check for Server-Side Code in a Browser Context

If the error originates from a third-party package, ensure that you are not importing a server-side module in a client-side script.
For example:

import fs from 'fs'; // ❌ This will fail in the browser

Instead, move such imports inside server-side logic or use conditional imports.

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Solution 6: Use vite-plugin-node-polyfills for Node.js Features in Vite

If your Vite project needs Node.js globals, install the polyfill:

npm install vite-plugin-node-polyfills --save-dev

Then modify vite.config.js:

import NodeGlobalsPolyfillPlugin from 'vite-plugin-node-polyfills';

export default {
  plugins: [
    NodeGlobalsPolyfillPlugin({
      process: true
    })
  ]
};

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Final Thoughts

• The process object is not available in the browser by default.
• Modern build tools like Webpack and Vite require manual polyfills for Node.js globals.
• If a library relies on process.env, use a define option or a polyfill.
• Always check whether you’re importing server-side code in a browser environment.

By following the above solutions, you can resolve the Uncaught ReferenceError: process is not defined error and ensure compatibility across different environments.