Environment variables are especially useful because we can avoid typing API keys and other sensible data in the code and have it pushed by mistake to GitHub.

And modern deployment platforms like Vercel and Netlify (and others) have ways to let us add environment variables through their interfaces.

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

Here is an example that accesses the NODE_ENV environment variable, which is set to development by default.

Note: process does not require a “require”, it’s automatically available

process.env.NODE_ENV // "development"


Setting it to “production” before the script runs will tell Node that this is a production environment.

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

Here we set 2 variables for API_KEY and API_SECRET

API_KEY=123123 API_SECRET=456456 node app.js

We can get them in Node.js by running

process.env.API_KEY // "123123"
process.env.API_SECRET // "456456"


You can write the environment variables in a .env file (which you should add to .gitignore to avoid pushing to GitHub), then

npm install dotenv

require('dotenv').config()
In this way you can avoid listing the environment variables in the command line before the node command, and those variables will be picked up automatically.
Note that some tools, like Next.js for example, make environment variables defined in .env automatically available without the need to use dotenv.