Unlocking the Power of Environment Variables in Next.js
Understanding Environment Variables
Environment variables are external values that developers define outside of the actual application code. These values can be used to influence the behavior of an application, and they often store sensitive data like API keys. Environment variables consist of name-value pairs, allowing an application to have different requirements when running in development, testing, and production environments.
The Role of Environment Variables in Next.js
Next.js, like most web frameworks, has built-in support for environment variables. You can declare environment variables in files such as .env.local, .env, env.development, and env.production. These files are not meant for storing secrets but for environment-specific configurations and settings.
Public and Private Environment Variables
Next.js environment variables can be categorized into public and private environment variables. Private environment variables are only accessible from the Node.js environment, while public environment variables are available both in the browser and Node.js environments. You can declare public environment variables by prefixing their name with NEXT_PUBLIC_.
Using Environment Variables in Local Development vs. Production
The requirements of an application while in development may not be the same as those in production. Therefore, some environment variables may only be required in development, others in production, and some in both environments. You can declare environment variables in different files, such as .env.development and .env.production, to cater to these different requirements.
Manipulating Environment Variables with next.config.js
Next.js offers flexible ways of working with environment variables. You can use the legacy env property of the next.config.js file to configure environment variables or the newer, more intuitive, and ergonomic .env* files.
Securely Storing Secrets for Local Development
During development, certain secrets such as API endpoints, usernames, passwords, API keys, database connection strings, and other credentials that are specific to your local development environment must not be exposed. In Next.js, you can securely store secrets in the .env.local file and add it to your .gitignore file to avoid checking it into a version control system like Git.
Dynamic Environment Variables in Next.js 13
Next.js will evaluate all references to environment variables and hardcode them in your client code at build time. If your frontend application needs access to dynamic environment variables at runtime, you should set up your own API and provide the variables to your client code.
Order of Environment Variable Lookup in Next.js
Next.js follows a specific order when looking for an environment variable, stopping after finding the variable it needs. The order includes process.env, env.${NODE_ENV}.local, env.local, env.${NODE_ENV}, and .env.
Interpolating Environment Variables in Next.js
In Next.js, you can create an environment variable by referencing or composing other environment variables using the ${VARIABLE_NAME} syntax. Next.js will expand and replace any referenced variable with its actual value.
By mastering environment variables in Next.js, you can write more flexible and maintainable code, ensuring your application behaves as expected in different environments.