Let's say you have the following files that make up your NodeJS app.

├── .env
├── package.json
├── app.js

And let's say the .env file contains variables, perhaps something like this.

FOO="hello"
BAR="world"

The dotenv package is used to read variables from a .env file. Your package.json file will need to include the dotenv dependency.

{
  "dependencies": {
    "dotenv": "^16.0.3"
  },
  "type": "commonjs"
}

And then in your app.js file, here is how you could use dotenv in console.log. Notice in this example that package.json has "type": "commonjs". WIth CommonJS, you will use require​.

require("dotenv").config()

console.log('The FOO variable contains a value of:', process.env.FOO);
console.log('The BAR variable contains a value of:', process.env.BAR);

Or better yet, create FOO and BAR constants.

require("dotenv").config()
const { FOO, BAR } = process.env;

console.log('The FOO variable contains a value of:', FOO);
console.log('The BAR variable contains a value of:', BAR);

If package.json had "type": "module" then app.js would have to use import (not require).

import "dotenv/config";
const { FOO, BAR } = process.env;

console.log('The FOO variable contains a value of:', FOO);
console.log('The BAR variable contains a value of:', BAR);

The console should contain something like this.

]$ node app.js
> NodeJS@1.0.0 start
The FOO variable contains a value of: hello
The BAR variable contains a value of: world