How to Read Environment Variables from Node.js

.env files are a popular method for managing application configuration outside the application code, often containing sensitive data such as API keys, database credentials, and other configuration settings. These are environment-specific, which means that developers can have it different. (local.env, dev.env, prod.env).

In this blog post, you will learn how to read the content of a .env file and unlock the full potential of this tool.

How to read .env in Node.js

The process core module of Node.js provides the env property which hosts all the environment variables that were set at the moment the process was started.

The below code runs app.js and set USER_ID and USER_PASSWORD.

USER_ID=MECAROGADMIN USER_PASSWORD=admin node app.js

That will pass the user USER_ID as MECAROGADMIN and the USER_PASSWORD as admin. This is suitable for testing, however for production, you will probably be configuring some bash scripts to export variables.

Note: process does not require a "require", it's automatically available.

Here is an example that accesses the USER_ID and USER_PASSWORD environment variables, which we set in above code.

process.env.USER_ID; // "MECAROGADMIN"
process.env.USER_KEY; // "admin"

In the same way you can access any custom environment variable you set.

Node.js 20 introduced experimental support for .env files.

Now, you can use the --env-file flag to specify an environment file when running your Node.js application. Here's an example .env file and how to access its variables using process.env.

# .env file
PORT=8080
SECRET_KEY=mysecretkey

In your js file

process.env.PORT; // "8080"
process.env.SECRET_KEY; // "mysecretkey"

Run app.js file with environment variables set in .env file.

node --env-file=.env app.js

This command loads all the environment variables from the .env file, making them available to the application on process.env

Also, you can pass multiple --env-file arguments. Subsequent files override pre-existing variables defined in previous files.

node --env-file=.env --env-file=development.env app.js

Note: if the same variable is defined in the environment and in the file, the value from the environment takes precedence.

.env variable is an important tool for professionals developers because it helps separation of concerns, security, portability, scalability, compatibility.