Next Js Dotenv Tutorial for Environment Variable Management

In Next.js, environment variables are crucial for managing sensitive data such as API keys and database credentials.

To get started with dotenv, create a .env file in the root directory of your project. This file will store your environment variables.

The .env file should not be committed to version control to prevent sensitive data from being exposed.

You can use the dotenv library to load environment variables from the .env file in your Next.js application.

To load environment variables in Next.js, you can create a .env.local file where you'll put all your environment variables for the local development environment. Next.js automatically adds this file to .gitignore so you don't have to worry about it ending up in your version control system.

To read the environment variables into your config, create a config.ts file with the necessary code.

The order of environment variable lookup in Next.js is as follows:

This order is crucial to understand, especially if you declare the same environment variable in multiple files. The environment variable declared in the lowest file in the list wins.

Encapsulating logic by creating a config for environment variables is a good practice, as it allows you to change how you get config values without touching the functionality at all.

This approach makes unit testing much easier, as you can mock the config with the values you want to test.

By encapsulating logic, you can keep your codebase clean and organized, and avoid relying on low-level abstractions like process.env.

Encapsulating logic helps to decouple code from low-level abstractions, making it easier to change how config values are retrieved without affecting the underlying functionality.

The logic of fetching blog posts doesn't care where it gets the api key from, so it shouldn't rely on process.env or any other low-level abstractions.

Creating a config for the sole purpose of reading environment variables encapsulates this functionality and creates a meaningful high-level abstraction.

This allows us to change the way we get the config values without touching the blog post functionality at all.

Unit testing becomes ten times easier with encapsulated logic, as we can mock the config with the values we want to test.

To protect your Next.js app and its environment variables, you can add a .env.local file to your .gitignore file to avoid checking it into a version control system like Git and pushing it to a cloud Git hosting service like GitHub.

Checking environment variables to a version control system may result in incurring significant costs if unknown individuals get access to your API keys or production database connection string.

You can share a template of the env.local file and its contents in a .env.local.example or .env.local.template file so that project contributors can set up their development environment using the file template.

Do not store secrets in other environment variables that are meant for storing non-secret information.

In Next.js, environment variables are looked up in a specific order, and the process is straightforward. This order is crucial for encapsulating logic and security in your application.

The first place Next.js looks for an environment variable is in the process.env object. This is the most direct way to access environment variables.

If the variable is not found in process.env, Next.js then checks for a file named env.${NODE_ENV}.local, where ${NODE_ENV} is the current environment (development, production, or test). This is a good place to put environment variables that are specific to a particular environment.

Next, Next.js checks for a file named env.local. However, if the current environment is test, this file is skipped. This is a security feature to prevent sensitive variables from being accidentally exposed in test environments.

If the variable is still not found, Next.js then checks for a file named env.${NODE_ENV}. This is another good place to put environment variables that are specific to a particular environment.

Finally, if all else fails, Next.js checks for a file named .env. This file is a catch-all for environment variables that don't have a specific environment or file associated with them.

Here's a summary of the variable lookup order:

Public environment variables are mostly used for storing constants or default values that you don’t want to import or declare in multiple files.

To make an environment variable public, you need to prefix its name with NEXT_PUBLIC_, as in the example where NEXT_PUBLIC_ENV_VARIABLE is declared.

At build time, Next.js will access and replace references to the public environment variables with their actual values in the codebase bundled for the browser environment.

Public environment variables are available both in the browser and in Node.js, making them a convenient option for storing values that need to be accessed across different environments.

Private environment variables, on the other hand, are only accessible from the Node.js environment and are private by default.

Interpolating environment variables is a powerful feature in Next.js, allowing you to create new variables by referencing or composing other variables using the ${VARIABLE_NAME} syntax.

This syntax expands and replaces any referenced variable with its actual value, avoiding repetition and keeping your environment variable files organized.

You can reference each environment variable independently from your codebase, making it easy to manage complex configurations.

Cross-file environment variable referencing is also possible in Next.js, enabling you to reference a variable declared in the env.local file from the .env file.

However, be aware of the order of environment variable lookup, as variables with similar names in different files can cause conflicts.

For example, referencing a variable declared in .env.development from .env.production won't work because those environment variables will only be available in their respective environments.