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🔧 React Environment Variables & .env Files – Secure App Configuration

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🧲 Introduction – Why Use Environment Variables in React?

When building React applications, you often need to store values that change per environment—like API URLs, Firebase keys, Stripe tokens, etc. React supports the use of .env files to manage such environment-specific configuration securely and flexibly.

Using environment variables ensures:

• 🔐 Secrets are not hardcoded
• 🔁 Configuration is easily swappable (dev, test, prod)
• 🔄 CI/CD pipelines remain clean and maintainable

🎯 In this guide, you’ll learn:

• How to define and access .env variables in React
• Best practices for .env.production and .env.local
• Common issues and security tips

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🛠️ 1. Environment File Structure in React

React supports multiple .env file types:

File Name	Purpose
.env	Default for all environments
.env.local	Local overrides, not committed to Git
.env.development	Used during npm start
.env.production	Used during npm run build
.env.test	Used during testing (npm test)

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✏️ 2. Defining Environment Variables

📁 Create a .env file in your project root:

REACT_APP_API_URL=https://api.example.com
REACT_APP_FIREBASE_KEY=AIzaSyExample

⚠️ Important:
React only exposes variables that begin with REACT_APP_.

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🧠 3. Accessing Environment Variables in Code

const apiUrl = process.env.REACT_APP_API_URL;

fetch(`${apiUrl}/users`)
  .then(res => res.json())
  .then(data => console.log(data));

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🚀 4. Production Variables with .env.production

Use .env.production for sensitive values or production-only URLs:

REACT_APP_API_URL=https://api.production.com

When running:

npm run build

React uses .env.production automatically.

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📦 5. Example Use Case

REACT_APP_MODE=development
REACT_APP_VERSION=1.2.3
REACT_APP_GOOGLE_ANALYTICS_ID=G-XXXXXXX

console.log("Mode:", process.env.REACT_APP_MODE);
console.log("Version:", process.env.REACT_APP_VERSION);

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🔐 6. Security & Deployment Tips

📘 Best Practice

• Use .env.local for sensitive values in development and gitignore it: .env.local

⚠️ Pitfall

• Do not store secrets like API keys, database passwords in React .env files unless you’re using server-side frameworks like Next.js.

💡 Tip

• On platforms like Netlify, Vercel, or Firebase, you can define environment variables via their web UI instead of .env files.

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🚫 7. Common Errors & Fixes

Error	Cause	Solution
undefined variable	Missing REACT_APP_ prefix	Add REACT_APP_ to all keys
Not updating after .env change	React uses cached vars	Restart dev server
Variables not loading in deployment	Host doesn’t recognize .env	Set vars in hosting dashboard

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📌 Summary – Recap & Next Steps

Environment variables help configure your React app cleanly and securely across different stages like development, testing, and production.

🔍 Key Takeaways

• Use .env files to manage external config
• Only variables prefixed with REACT_APP_ are exposed
• .env.production is used during npm run build
• Never hardcode secrets in public apps

⚙️ Real-World Relevance:
React environment variables are used in apps like e-commerce stores, SaaS dashboards, and Firebase-based tools to keep APIs dynamic and deployment-specific.

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❓ FAQ – React Environment Variables

❓ Why does React require REACT_APP_ prefix?
✅ It prevents accidental exposure of private variables to the browser.

❓ Can I access .env values inside HTML?
🚫 No. They’re only available in JavaScript files.

❓ Do I need to restart the server after changing .env?
✅ Yes. React reads .env at compile time, so restart with npm start.

❓ Can I have multiple .env files in one project?
✅ Yes. Use .env, .env.local, .env.production, etc., as needed.

❓ Is it safe to store Firebase keys in .env?
⚠️ Partially. Firebase keys used in frontend are public, so apply Firestore security rules to restrict usage.

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