Environment variables are a crucial part of any application, especially when it comes to managing configuration settings that can change between different environments (development, testing, production). In this section, we will cover what environment variables are, how to use them in Node.js, and best practices for managing them.

Environment variables are key-value pairs that are used to configure settings for your application. They are typically used to store sensitive information such as API keys, database connection strings, and other configuration settings that should not be hard-coded into your application.

• Environment Variables: Key-value pairs used to configure application settings.
• Environment: The context in which your application runs (e.g., development, testing, production).

You can set environment variables in the command line using the set command:

You can set environment variables in the terminal using the export command:

A common practice is to use a .env file to store environment variables. This file is then loaded into your application using a package like dotenv.

Example .env file:

To access environment variables in a Node.js application, you can use process.env. This is a global object that provides access to the environment variables.

1. Loading Environment Variables: The dotenv package is used to load environment variables from a .env file into process.env.
2. Accessing Variables: Environment variables are accessed using process.env.VARIABLE_NAME.
3. Default Values: You can provide default values using the || operator.

1. Do Not Hard-Code Sensitive Information: Always use environment variables for sensitive information like API keys and database credentials.
2. Use a .env File for Local Development: Store environment variables in a .env file for local development and use a package like dotenv to load them.
3. Keep .env Files Out of Version Control: Add .env files to your .gitignore to prevent them from being committed to version control.
4. Use Environment-Specific Configuration: Use different environment variables for different environments (development, testing, production).

Create a simple Node.js application that reads environment variables from a .env file and prints them to the console.

1. Initialize a Node.js Project:

   mkdir env-demo
   cd env-demo
   npm init -y
   npm install dotenv
   

2. Create a .env File:

   touch .env
   

   Add the following content to the .env file:

   PORT=3000
   DATABASE_URL=mongodb://localhost:27017/mydatabase
   API_KEY=your_api_key_here
   

3. Create an index.js File:

   touch index.js
   

   Add the following content to the index.js file:

   require('dotenv').config();
   
   const port = process.env.PORT || 3000;
   const databaseUrl = process.env.DATABASE_URL;
   const apiKey = process.env.API_KEY;
   
   console.log(`Server will run on port: ${port}`);
   console.log(`Database URL: ${databaseUrl}`);
   console.log(`API Key: ${apiKey}`);
   

4. Run the Application:

   node index.js
   

The output should display the values of the environment variables defined in the .env file.

• Forgetting to Load Environment Variables: Ensure you call require('dotenv').config() at the beginning of your application.
• Incorrect Variable Names: Environment variable names are case-sensitive. Make sure you use the correct names.
• Not Adding .env to .gitignore: Always add your .env file to .gitignore to prevent sensitive information from being committed to version control.

In this section, we learned about environment variables, how to set them, and how to use them in a Node.js application. We also covered best practices for managing environment variables and provided a practical exercise to reinforce the concepts. Understanding and properly managing environment variables is crucial for building secure and configurable applications.