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How to Use Environment Variables Like a Pro in Node.js

Environment variables can be created on the application or system level.


Bewar Salah

4 months ago | 3 min read



There are many constant values that need to be stored in applications and retrieved for later use, like DB username, DB password, email password, and API Keys. These values may change in different circumstances.

When a developer writes a piece of code, the code needs to be tested. The tests should be against the development environment. The developer should not connect to a production DB server.

The developer usually uses a local database for developing and testing, a personal email account to send test emails. Sometimes, before production deployment, the app goes to the staging environment and is tested by the Quality Assurance (QA) team against the staging environment.

Finally, in the production environment, all services should be ready for production. For that reason, we need to maintain two or more environments while creating applications.

It is convenient and conventional to store some constant values which differ during the environment change. The application can be configured to retrieve these values based on the environment it is running on.
Environment Variables

Environment variables can be created on the application or system level.

Different Levels

Operating systems like Windows and Linux manage their own environment variables. Node.js application can read these values from the hosting system.

But wait! What if the developer wants to read these values locally stored in a file instead (for example, a configuration file)?

Node.js applications can also manage their own environment variables stored in a file (called configuration file in most other programming languages). Node.js cannot maintain the local environment variables by itself. It has to use a package called dotenv.

dotenv reads from .env

The package dotenv can be installed using an NPM command and it reads from a file called .env .

Set Up an Application

To understand the whole concept, we are going to create a Node.js server running on multiple environments to demonstrate the usage of dotenv node package for maintaining local variables, and also try to deploy on a server to read system variables while running on the server.

Steps for setting up the application:

  • Creating package.json file

npm init -y

  • Installing dotenv

npm i -S dotenv

  • Calling dotenv config function on the top of the application


  • Creating .env file in the root of the application with the following content

.env file

  • Accessing the values using process.env

const DB_HOST = process.env.DB_HOST;

const DB_USER = process.env.DB_USER;

Now, if we run the application locally, dotenv reads these values from .env file and attached to process.env object. If .env does not exist, node.js tries to read these values from the machine environment variables.

The below application reads the values from .env and return it to the user.

complete node.js server

Deploying on Heroku

We are going to deploy the application on Heroku, and explain how to read these values from system variables.

There are multiple ways to deploy applications on Heroku. We are going to use the GitHub method.


  • Github account
  • Heroku account
  • Git installed on a working machine

Steps to deploy

  1. Create a GitHub account and create a new git repository.

New Repository

The name of the repository should be filled in our case, it is env_demo. If the project is private, you need to select Private option.

github — new repository

2. We need to make some changes in package.json.

  • add engines and specify node version — this is required for Heroku to install the node for the app.
  • add start script node index, Heroku runs npm start for Node.js apps.



: "env_demo",


: "1.0.0",


: "",


: "index.js",


: {


: "node index",


: "echo \"Error: no test specified\" && exit 1"



: {


: "14.x"



: [],


: "",


: "ISC",


: {


: "^10.0.0"



Also, we need to specify the port to run the app in index.js file as below. This is required by Heroku. You should not specify the port.








) {


.writeHead(200, { "Content-Type": "application/json" });









3. Add a file named .gitignore, in the root directory of the project. We can specify the files that should not be uploaded to the GitHub server.

In our instance, we don’t want to add .env, as it contains my personal details and node_modules directory as it is not recommended, Heroku creates node_modules and fetches the required npm packages.

.gitignore file

4. In the project directory on your machine, write the below commands.

git init

git add .

git commit -m "initial commit"

git remote add origin

git push origin master

5. Go to Heroku and create an account

6. Create a new app

heroku — create new app

7. Choose Connect to Github from the deploy tab.

heroku — connect to github

8. Find the repository and choose to Connect, then click Deploy Branch. After the deployment is completed, click on the View button, to see the app in the browser.

heroku — connect

heroku — deploy branch

Now the app opens and displays an empty JSON object. Why? because we did not specify the environment variables in the Heroku ecosystem.

node — reading env variables

Configuring Variables

  • In the settings tab, click on Reveal Config Vars.
  • Add the variables there.

heroku — config vars

  • and testing...


It is very crucial in application development to separate multiple environment variables. Maintaining multiple environment variables is easy in a Node.js application with the usage of the npm package dotenv. It reads from a file called .env.

While a .env file does not exist, process.env tries to read from the machine environment variables.

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Created by

Bewar Salah


Software Developer







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