How to Set Up a .env File with Node.js, Deno or Bun

Each runtime has it's own way of handling the .env file, we will see how to do it with Node.js, Deno and Bun

Setup

Create a .env file we will be loading into our runtime environment and add some variables to it in the following format: VAR_NAME=value

For example:

DB_HOST = localhost
DB_USER = admin
DB_PASS = password123

Node.js

Loading the .env file

Now that we created this file we need to load it into the environment variables of the node process, we have 2 alternative

1. Use the build-in --env-file option (requires Node.js v20.6+)
2. Use the dotenv package

--env-file option

You need to update the command line you use for running node with the following node option and passing it the file name for the .env file, the file is resolved based on the directory you are running node from

Here is an example:

node --env-file=.env index.js

You need to add this flag before the file you want to run also if you have multiple .env file you want to include you can add multiple --env-file

dotenv package

If you don't want or can't use the --env-file option you can do it with the dotenv package

First of all you need to install the dotenv package along it's type if you are using TypeScript

npm install dotenv @types/dotenv --save-dev or using yarn, pnpm or bun

We now need to load the .env from our code so let's add the following code to your typescript file:

import dotenv from 'dotenv'

dotenv.config()

This will import the dotenv module and add all the variables we declared in our .env file into the node environment variables

Use the environment variables

You can now access your environment variables using the process.env object. For example:

const dbHost = process.env.DB_HOST
const dbUser = process.env.DB_USER
const dbPass = process.env.DB_PASS

And that's it! You have now set up a .env file in Node.js and can access your environment variables in your code.

Deno

Deno has a function in the standard library to load the env from a .env file so we will use that function to load our .env file

Loading the .env file

We first need to import the load function from the dotenv module of the standard library and then call it, by doing this it will return us with the environment variables that exited inside the .env file.

import { load } from 'https://deno.land/std@0.212.0/dotenv/mod.ts'

const env = await load()

Use the environment variables

With the return object returned by load we can access the environment variables it just obtained. For example:

const dbHost = env.DB_HOST
const dbUser = env.DB_USER
const dbPass = env.DB_PASS

And that's it! You have now set up a .env file in Deno and can access your environment variables in your code.

Bun

Bun automatically detects and load all the .env file in the current directory where you run the bun command. Bun actually allows for some configuration of the runtime itself from this .env file and some additional options. You can refer to the Bun documentation to see them

Loading the .env file

We just need to have the .env in the same directory as the current directory from where we run the bun command.

If you need you can specify one or more --env-file options with the path to your .env file if you need it.

Using the environment variables

Since Bun aims to be a Drop-in replacement for Node.js we can use it's own Bun.env object to access the environment variables or just use the process.env object to do so.

For example using Bun.env:

const dbHost = Bun.env.DB_HOST
const dbUser = Bun.env.DB_USER
const dbPass = Bun.env.DB_PASS

Or using process.env:

const dbHost = process.env.DB_HOST
const dbUser = process.env.DB_USER
const dbPass = process.env.DB_PASS

And that's it! You have now set up a .env file in Bun and can access your environment variables in your code.