How to Pass Environment Variables in Next.js Deployments

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Environment variables are a critical part of modern web development. They help keep sensitive information like API keys, database credentials, and configuration settings secure while providing flexibility to manage different environments such as development, testing, and production. In Next.js, managing environment variables is straightforward yet powerful. This guide will help you understand how to use environment variables effectively in next js env variables projects.

What Are Environment Variables?

Environment variables are key-value pairs that are used to configure application behavior without hardcoding sensitive data into the codebase. They allow developers to store settings separately from the code, making applications more secure, maintainable, and adaptable to various environments.

For example, instead of embedding an API key directly into your JavaScript file, you can store it as an environment variable and access it dynamically in your application.

How Next.js Handles Environment Variables

Next.js provides a robust way to handle environment variables, ensuring they can be used securely and efficiently across your application. Here are some key points to understand:

  1. Environment File Naming Conventions
    Next.js supports the use of .env files to store environment variables. Depending on the environment, you can use the following files:

    • .env: Loaded in all environments.
    • .env.local: Loaded in all environments but ignored by version control (useful for secrets).
    • .env.development: Loaded only in the development environment.
    • .env.production: Loaded only in the production environment.
    • .env.test: Loaded only during testing.

    These files are loaded in a cascading manner, with more specific files overriding the general ones.

  2. Client-Side vs. Server-Side Variables
    By default, all environment variables are available only on the server side for security reasons. To expose a variable to the client, you must prefix it with NEXT_PUBLIC_. For example:

    env
    NEXT_PUBLIC_API_URL=https://api.example.com

    This ensures sensitive variables remain secure and are not accidentally exposed to the browser.

  3. Accessing Environment Variables
    In Next.js, you can access environment variables using the process.env object. For example:

    javascript
    const apiUrl = process.env.NEXT_PUBLIC_API_URL;
    console.log(apiUrl); // https://api.example.com

Using Environment Variables in Next.js

1. Setting Up Environment Variables

  • Create a .env.local file in the root of your Next.js project.
  • Add your key-value pairs in the file:
    env
    NEXT_PUBLIC_API_URL=https://api.example.com
    SECRET_API_KEY=supersecretkey

2. Accessing Server-Side Variables

Server-side variables (those without the NEXT_PUBLIC_ prefix) can only be used in server-side code like API routes, getServerSideProps, or getStaticProps:

javascript
export async function getServerSideProps() {
const secretKey = process.env.SECRET_API_KEY;
return {
props: { key: secretKey },
};
}

3. Using Client-Side Variables

For variables prefixed with NEXT_PUBLIC_, you can use them in components or client-side code:

javascript
export default function Home() {
const apiUrl = process.env.NEXT_PUBLIC_API_URL;
return <p>API URL: {apiUrl}</p>;
}

4. TypeScript Support

If you’re using TypeScript, you can define types for environment variables to prevent errors. Create a next-env.d.ts file and extend the NodeJS.ProcessEnv interface:

typescript
namespace NodeJS {
interface ProcessEnv {
NEXT_PUBLIC_API_URL: string;
SECRET_API_KEY: string;
}
}

Best Practices for Environment Variables in Next.js

  1. Keep Secrets Secure
    Never expose sensitive information (e.g., API keys, database credentials) in the client. Use server-side code for handling sensitive data.
  2. Use .env.local for Local Development
    Store local, environment-specific variables in .env.local, and ensure this file is added to your .gitignore to avoid committing secrets to your repository.
  3. Separate Environments
    Use environment-specific files (.env.production, .env.development) to maintain clarity and avoid mixing configurations.
  4. Avoid Hardcoding Values
    Always reference environment variables using process.env. Hardcoding makes maintenance harder and reduces flexibility.
  5. Validate Variables
    Consider validating environment variables at runtime to ensure required keys are set. A library like dotenv-safe can help with this.
  6. Use Deployment Tools
    If deploying to platforms like Vercel, use their integrated environment variable management system to securely define variables for each environment.

Debugging Environment Variables

If your variables aren’t behaving as expected:

  • Ensure your .env file is correctly named and located in the root directory.
  • Restart your development server after making changes to .env files.
  • Use console.log(process.env) to debug available variables. Be cautious not to log sensitive data.

Environment variables in Next.js provide a powerful way to manage configurations and keep sensitive information secure. By understanding their nuances—such as file naming conventions, client-server distinction, and best practices—you can build more secure and maintainable applications. Whether you’re working on a personal project or a large-scale production app, mastering environment variables in Next.js is an essential skill for every developer.

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