Dotenv tutorial
last modified October 18, 2023
In this article we show how to load environment variables in JavaScript using the dotenv module.
The dotenv module
The dotenv is a zero-dependency module that loads environment
variables from a .env file into process.env.
Storing configuration in the environment separate from code is based on
the Twelve-Factor App methodology.
Environment variables
Environment variables allow us to manage the configuration of our applications separately from our codebase. Separating configurations makes it easier for our application to be deployed in different environments.
Environment variables are variables external to our application which reside
in the OS or the container where the production application is running. Because
development is mostly done on local machines, environment variables are put
either to local environment variables with commands such as set
or export, or stored in the local .env file.
By convention, the variables are written in uppercase letters (e.g. PORT).
Common examples of configuration data that are stored in environment variables include:
- HTTP port
- database connection string
- location of static files
- endpoints of external services
The .env file should never be committed to the source code repository. We
must place the file into the .gitignore file. (When using git.)
Modern editors have support for .env files; for instance, the code
has the DotENV extension.
The .env parsing rules
Here are some basic parsing engine rules:
- BASIC=basic becomes {BASIC: 'basic'}
- empty lines are skipped
- comments start with #
- empty values become empty strings; BASIC= becomes {BASIC: ''}
- inner quotes are maintained
Existing environment variables are not modified; they are skipped.
Dotenv set up
We install the dotenv module with npm.
$ node -v v11.5.0
We use Node version 11.5.0.
$ npm init -y
We initiate a new Node application.
$ npm i dotenv
We install dotenv with npm i dotenv command.
Dotenv simple example
In the first example, read configuration data from the
.env file.
HOST = localhost DATABASE = ydb PORT = 5432
We have three variables: HOST, DATABASE, and
PORT. We adhere to the naming convention by using uppercase
letters.
require('dotenv').config()
const hostname = process.env.HOST;
const database = process.env.DATABASE;
const port = process.env.PORT;
console.log(hostname);
console.log(database);
console.log(port);
In the example, we read the three variables and print them to the console.
require('dotenv').config()
We load the dotenv library and call the config
method, which loads the variables into the process.env.
const hostname = process.env.HOST; const database = process.env.DATABASE; const port = process.env.PORT;
We read the three variables from process.env.
console.log(hostname); console.log(database); console.log(port);
Finally, the variables are printed to the terminal.
$ node simple.js localhost ydb 5432
Dotenv preloading
We can use the --require (-r) command line option to preload dotenv.
By doing this, we do not need to require and load dotenv in the application.
HOST = localhost DATABASE = ydb PORT = 5432
We have the same variables.
const hostname = process.env.HOST; const database = process.env.DATABASE; const port = process.env.PORT; const user = process.env.USER; console.log(hostname); console.log(database); console.log(port); console.log(user);
In this example, we do not require the dotenv module.
In addition, we read a variable that is set in the OS environment.
$ set USER=user7 $ node -r dotenv/config preload.js localhost ydb 5432 user7
On Windows, we use set to define environment variables.
(Use export on Linux). The variables are printed OK.
Source
In this article we have used the dotenv module to read environment variables
from the .env file.