Process.env variables undefined in frontend code

If process.env variables are undefined in frontend JavaScript code, it is because process.env is a feature of Node.js, which runs on the backend. The browser does not have direct access to environment variables the same way a Node.js application does.

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Step 1: Understanding process.env

In Node.js, process.env is an object that contains the environment variables available to the application. It is used to store sensitive data like API keys, database URLs, and configuration settings.

Example in a Node.js backend:

console.log(process.env.MY_SECRET_KEY);

If you run this in a Node.js environment, it will log the value of MY_SECRET_KEY, assuming it’s defined in your .env file or system environment.

However, in the frontend (browser), process.env does not exist by default. If you try to log process.env in a browser console, you’ll see undefined.

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Step 2: Why is process.env Undefined in Frontend JavaScript?

Since process.env is part of the Node.js runtime, it is not automatically available in browser-side JavaScript. When you run frontend code in the browser:

• The browser does not have access to the server’s environment variables.
• JavaScript running in the browser is not a Node.js environment.
• process.env is not a native JavaScript feature outside of Node.js.

Example Problem in Frontend Code

console.log(process.env.API_KEY); // undefined

Since process.env is a Node.js feature, it won’t work in the browser.

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Step 3: How to Fix process.env in Frontend Code?

To use environment variables in a frontend project, you need a way to expose them during the build process. Below are different solutions depending on your frontend setup.

Solution 1: Using Vite for Environment Variables

If you are using Vite, environment variables must start with VITE_ and should be stored in a .env file.

Steps:

1. Create a .env file in your project root: VITE_API_KEY=123456789
2. Access the variable in your frontend code: console.log(import.meta.env.VITE_API_KEY);
3. Restart the development server (npm run dev).

Solution 2: Using Create React App (CRA)

If you are using Create React App, you need to prefix environment variables with REACT_APP_.

Steps:

1. Create a .env file in your React project: REACT_APP_API_KEY=123456789
2. Access it in your components: console.log(process.env.REACT_APP_API_KEY);
3. Restart your React server (npm start).

Solution 3: Using Webpack or Next.js

In Webpack or Next.js, you can define environment variables using Webpack’s DefinePlugin or Next.js next.config.js.

For Webpack

Modify your webpack.config.js:

const webpack = require('webpack');

module.exports = {
  plugins: [
    new webpack.DefinePlugin({
      'process.env.API_KEY': JSON.stringify(process.env.API_KEY),
    }),
  ],
};

For Next.js

Next.js has built-in support for environment variables.

1. Create a .env.local file: NEXT_PUBLIC_API_KEY=123456789
2. Use it in your frontend code: console.log(process.env.NEXT_PUBLIC_API_KEY);
3. Restart the Next.js server (npm run dev).

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Step 4: Common Mistakes and How to Avoid Them

1. Forgetting to Restart the Development Server
   After adding or modifying .env files, always restart the server.
2. Using Wrong Prefix (for Vite, CRA, Next.js, etc.)
   • VITE_ for Vite
   • REACT_APP_ for Create React App
   • NEXT_PUBLIC_ for Next.js
3. Trying to Access Backend Variables in the Frontend
   • Do not expose sensitive keys like database passwords in frontend code.
   • Use a backend API to securely fetch such data.
4. Not Adding .env to .gitignore
   • Always add .env to your .gitignore file to prevent exposing secrets in version control.

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Step 5: Debugging Tips

1. Check if process.env is available in Node.js console.log(process.env); If this works in a Node.js script but not in your frontend, the issue is related to how environment variables are being exposed.
2. Print import.meta.env in Vite console.log(import.meta.env); This will show all environment variables available in Vite.
3. Check .env file formatting
   • No spaces around =: VITE_API_KEY=123456789 ✅ VITE_API_KEY = 123456789 ❌
   • No quotes ("123456789" or '123456789' is incorrect).
4. Use console.log to debug the value console.log("API Key:", process.env.REACT_APP_API_KEY || "Not Defined"); If Not Defined appears, check if .env is correctly loaded.

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Final Thoughts

• process.env is a backend feature and is undefined in frontend JavaScript unless explicitly exposed.
• Use .env files with the correct framework-specific prefix (VITE_, REACT_APP_, NEXT_PUBLIC_).
• Always restart the server after modifying .env.
• Never expose sensitive environment variables directly in the frontend.

By following these steps, you should be able to use environment variables correctly in your frontend JavaScript applications!