Environment Variables in Next.js: A Comprehensive Guide

Environment variables are crucial for managing configuration and secrets in software development. Next.js, a popular React framework, provides robust support for environment variables, enabling developers to securely store and access sensitive information. This blog post will delve into the concepts and best practices of working with environment variables in Next.js applications.

What are Environment Variables?

Environment variables are key-value pairs that store configuration data outside of the application code. They are typically set during deployment or when the application is started. Environment variables are accessible within the application runtime and can be used to control various aspects of the application, such as:

• Database connection strings
• API keys
• Secret credentials
• Feature flags

Configuring Environment Variables in Next.js

Next.js provides several ways to configure environment variables:

• .env Files: .env files are plain text files that contain environment variable definitions. Next.js automatically loads environment variables from .env files located in the root directory of the application.
• process.env Object: The process.env object is a global object that contains all available environment variables. Developers can access environment variables by using the process.env.<variable_name> syntax.
• Next.js Config: Environment variables can also be defined within the Next.js configuration file (next.config.js). However, this approach is not recommended for storing sensitive information, as environment variables defined in this way will always be included in the JavaScript bundle.
  To add environment variables to the JavaScript bundle, open next.config.js and add the env config:

    // next.config.js
  
  module.exports = {
    env: {
      customKey: 'my-value',
    },
  };
    

  Now you can access process.env.customKey in your code. For example:
  

  
  function Page() {
    return <h1>The value of customKey is: {process.env.customKey}</h1>;
  }
  
  export default Page;
    

  Next.js will replace process.env.customKey with 'my-value' at build time.

Exposing Environment Variables to the Browser

By default, environment variables are only available on the server. To expose an environment variable to the browser, it must be prefixed with NEXT_PUBLIC_. However, these public environment variables will be inlined into the JavaScript bundle during the Next.js build process. This means that any sensitive information stored in public environment variables will be accessible to anyone who can view the source code.

Best Practices for Environment Variables

• Use Consistent Naming Conventions: Establish clear naming conventions for environment variables to ensure consistency and ease of maintenance.
• Avoid Hard-Coding Secrets: Never hard-code sensitive information in the application code. Instead, use environment variables to store and retrieve secrets securely.
• Separate Environment Files: Create separate .env files for different environments (e.g., development, staging, production) to manage configuration settings specific to each environment.
• Use Variable Expansion: Next.js supports variable expansion in .env files, allowing developers to reference other environment variables in their definitions.
• Keep Secrets Out of Source Control: Avoid committing .env files containing sensitive information to source control repositories. Use tools like .gitignore to exclude these files.

Conclusion

Environment variables are an essential aspect of modern software development. Next.js provides flexible and secure mechanisms for managing environment variables, enabling developers to efficiently store and access configuration data and secrets. By following the best practices outlined in this guide, developers can ensure the confidentiality, integrity, and availability of their Next.js applications.