How to read environment variables from 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 sets USER_ID and USER_KEY.

USER_ID=239482 USER_KEY=foobar node app.js

That will pass the user USER_ID as 239482 and the USER_KEY as foobar. 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_KEY environment variables, which we set in above code.

process.env.USER_ID; // "239482
process.env.USER_KEY; // "foobar

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=3000

In your js file

process.env.PORT; // 3000

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.