dotenv for environment configuration in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the dotenv package in Node.js?

dotenv loads environment variables from a .env file into process.env, allowing you to keep configuration separate from code.

beginner

How do you load environment variables using dotenv in a Node.js project?

You require dotenv and call dotenv.config() at the start of your application to load variables from the .env file into process.env.

beginner

What should you NOT do with your .env file in a project?

You should NOT commit your .env file to version control because it may contain sensitive data like API keys or passwords.

beginner

How can you access an environment variable named API_KEY in your Node.js code after using dotenv?

You access it with process.env.API_KEY, which returns the value as a string or undefined if not set.

intermediate

Why is using dotenv helpful when working on a team or deploying an app?

dotenv helps keep environment-specific settings outside code, so each developer or server can have its own config without changing the codebase.

What file does dotenv read to load environment variables?

A package.json

B .env

C config.json

D settings.js

dotenv reads the .env file by default to load environment variables.

Which method do you call to load variables from .env using dotenv?

A dotenv.config()

B dotenv.init()

C dotenv.start()

D dotenv.load()

The correct method to load environment variables is dotenv.config().

Where are environment variables stored after loading with dotenv?

A global.env

B window.env

C process.env

D module.exports

Environment variables are stored in process.env in Node.js.

Why should you add .env to your .gitignore file?

A To share environment variables with the team

B To prevent large files from being committed

C To speed up git operations

D To avoid committing sensitive information

The .env file often contains sensitive data, so it should not be committed to version control.

If process.env.API_KEY is undefined, what does it mean?

A API_KEY is not defined in the environment

B API_KEY is set to an empty string

C dotenv failed to load

D API_KEY is a number

If process.env.API_KEY is undefined, it means the variable was not set in the environment or .env file.

Explain how dotenv helps manage environment variables in a Node.js project.

Think about how you keep secrets or settings outside your code.

Describe best practices for using a .env file safely in a team project.

Consider security and collaboration.

Practice

1. What is the main purpose of using dotenv in a Node.js project?

easy

A. To manage database connections automatically

B. To compile JavaScript code faster

C. To load environment variables from a file into process.env

D. To create HTTP servers easily

Solution

1. Step 1: Understand what dotenv does

   dotenv reads a file (usually .env) and loads variables into process.env.

2. Step 2: Identify the main purpose

   This allows your app to access secret or environment-specific settings safely without hardcoding them.

3. Final Answer:

   To load environment variables from a file into process.env -> Option C

4. Quick Check:

   dotenv loads env vars = C [OK]

Hint: dotenv loads .env variables into process.env [OK]

Common Mistakes:

• Thinking dotenv compiles or runs code
• Confusing dotenv with database or server tools
• Expecting dotenv to manage app logic

2. Which of the following is the correct way to load environment variables using dotenv in a Node.js file?

easy

A. require('dotenv').config()

B. import dotenv from 'dotenv'; dotenv.load()

C. dotenv.setup()

D. require('dotenv').loadEnv()

Solution

1. Step 1: Recall the dotenv usage syntax

   The official and common way to load variables is calling require('dotenv').config() at the start of your app.

2. Step 2: Check other options for correctness

   The other options use incorrect method names or syntax not supported by dotenv.

3. Final Answer:

   require('dotenv').config() -> Option A

4. Quick Check:

   Use config() method to load dotenv [OK]

Hint: Use require('dotenv').config() to load env vars [OK]

Common Mistakes:

• Using wrong method names like load or setup
• Forgetting to call config() function
• Trying to import dotenv without config call

3. Given the following code and .env file, what will be the output?

// .env file content
API_KEY=12345
PORT=8080

require('dotenv').config();
console.log(process.env.API_KEY);
console.log(process.env.PORT);

medium

A. undefined\nundefined

B. null\nnull

C. API_KEY\nPORT

D. 12345\n8080

Solution

1. Step 1: dotenv loads variables from .env into process.env

   After calling require('dotenv').config(), process.env.API_KEY is set to "12345" and process.env.PORT is set to "8080" as strings.

2. Step 2: console.log prints the values

   The console will output the values exactly as strings, separated by new lines.

3. Final Answer:

   12345 8080 -> Option D

4. Quick Check:

   dotenv loads vars as strings = 12345\n8080 [OK]

Hint: dotenv sets process.env vars as strings from .env [OK]

Common Mistakes:

• Expecting numbers instead of strings
• Not calling config() before accessing vars
• Assuming variables are undefined without loading dotenv

4. What is the error in the following code snippet that prevents environment variables from loading correctly?

const dotenv = require('dotenv');
dotenv.config;
console.log(process.env.SECRET_KEY);

medium

A. Missing parentheses after config function call

B. dotenv package not installed

C. SECRET_KEY not defined in .env file

D. Using require instead of import

Solution

1. Step 1: Check how dotenv.config is called

   The code uses dotenv.config; without parentheses, so the function is not executed.

2. Step 2: Understand the effect of missing parentheses

   Without calling config(), environment variables are not loaded into process.env, so SECRET_KEY remains undefined.

3. Final Answer:

   Missing parentheses after config function call -> Option A

4. Quick Check:

   Call config() with () to load env vars [OK]

Hint: Always call config() with parentheses to load env [OK]

Common Mistakes:

• Forgetting parentheses on config function
• Assuming require auto-executes config
• Ignoring missing .env file or variable

5. You want to use dotenv to load different environment variables for development and production. Your .env file has NODE_ENV=development and API_URL=http://localhost:3000. You also have a .env.production file with NODE_ENV=production and API_URL=https://api.example.com. How can you load the correct file based on the environment?

hard

A. Use dotenv.loadEnv(process.env.NODE_ENV) to auto-load

B. Call require('dotenv').config({ path: `.env.${process.env.NODE_ENV}` }) after setting NODE_ENV

C. Rename .env.production to .env manually before running

D. Call require('dotenv').config() only once without options

Solution

1. Step 1: Understand dotenv supports custom paths

   dotenv's config function accepts a path option to specify which file to load.

2. Step 2: Use NODE_ENV to select the file dynamically

   By calling require('dotenv').config({ path: `.env.${process.env.NODE_ENV}` }), you load .env.development or .env.production based on the environment.

3. Final Answer:

   Call require('dotenv').config({ path: `.env.${process.env.NODE_ENV}` }) after setting NODE_ENV -> Option B

4. Quick Check:

   Use config({ path }) to load env files by environment [OK]

Hint: Use config({ path: `.env.${NODE_ENV}` }) to load env files [OK]

Common Mistakes:

• Not specifying path option for different env files
• Manually renaming files instead of dynamic loading
• Using nonexistent dotenv.loadEnv method