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Lesson 43 of 59

What Are Environment Variables in React? How to Use Them Securely Across Development, Build, and Production

Environment variables in React are configuration values used to control application behavior without hardcoding sensitive or environment-specific data into the source code. They are commonly used to manage API URLs, feature flags, analytics keys, and environment-based logic across development, staging, and production environments. Unlike backend environment variables, React environment variables are embedded into the build at compile time, making them accessible in the browser but also introducing important security considerations. This guide explains what environment variables are, how they work internally in React, how to define and access them correctly, differences between build tools, common mistakes, security risks, real-world production patterns, and best practices for scalable frontend applications.

Why Environment Variables Are Critical in React Applications

Modern React applications rarely operate in a single environment. They usually run across development, staging, QA, and production, each requiring different configurations.

Hardcoding values such as API URLs, analytics keys, or feature flags creates security risks, complicates deployments, and makes applications difficult to scale.

Production systems like large configuration-driven platforms depend heavily on environment variables to control behavior safely and predictably.

What Are Environment Variables?

Environment variables are key-value pairs used to store configuration outside the application’s source code.

In React, environment variables are:

  • Read at build time, not runtime
  • Injected into the JavaScript bundle
  • Accessible via process.env

This distinction is critical for understanding both their power and their limitations.

How Environment Variables Work Internally in React

When a React app is built:

  • The bundler reads environment variables
  • Values are statically replaced in the code
  • The final bundle contains those values

This means:

  • Changing environment variables requires rebuilding
  • Variables are visible in the browser
  • They are NOT secrets in frontend apps

Environment Variables in Create React App (CRA)

Naming Rules

In Create React App, environment variables must:

  • Start with REACT_APP_
  • Be defined in a .env file or system environment

Example .env File


REACT_APP_API_URL=https://api.example.com
REACT_APP_ENV=production

Accessing Variables in Code


const apiUrl = process.env.REACT_APP_API_URL;

These variables are commonly used to switch endpoints in flows like dynamic form submission pipelines.

Environment Variables in Vite and Modern Build Tools

Key Differences from CRA

  • Uses import.meta.env
  • Prefix is VITE_
  • Faster build-time injection

Example


VITE_API_URL=https://api.example.com

const apiUrl = import.meta.env.VITE_API_URL;

Common Use Cases for Environment Variables

  • API base URLs
  • Feature flags
  • Build-time environment detection
  • Third-party service keys (non-secret)

Feature toggles controlled via environment variables are often discussed in frontend system design articles.

Environment Variables vs Runtime Configuration

Aspect Environment Variables Runtime Config
When evaluatedBuild timeRuntime
SecurityPublicCan be private
Rebuild neededYesNo

Security Considerations (Very Important)

Never store secrets in React environment variables.

This includes:

  • API private keys
  • Database credentials
  • JWT secrets

Anything placed in a React environment variable is visible in the browser’s source code.

Real-World Production Example

Consider a React app deployed across environments:

  • Development uses local APIs
  • Staging uses testing servers
  • Production uses live services

Environment variables control:

  • Which API is called
  • Which features are enabled
  • Which analytics are active

This pattern is standard in scalable apps and evaluated through architecture-based assessments.

Common Mistakes Developers Make

  • Forgetting the required prefix
  • Expecting runtime changes to work
  • Storing secrets in frontend env files
  • Not restarting the dev server after changes

Best Practices & Special Notes

  • Keep environment variables minimal
  • Document all required variables
  • Use environment variables only for configuration
  • Combine with backend secrets for security

Final Takeaway

Environment variables in React are powerful but often misunderstood. They enable flexible configuration across environments, but they are not a security mechanism. Understanding their build-time nature, limitations, and correct usage is essential for building scalable, secure, and production-ready React applications.