Environment configuration in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the purpose of the .env file in a Node.js project?

Choose the best explanation for why developers use a .env file in Node.js projects.

A To define the structure of the database used by the application.

B To write the main application logic and server code.

C To list all installed Node.js packages and their versions.

D To store environment-specific configuration variables securely outside the codebase.

💡 Hint

Think about how you keep secret keys or settings separate from your code.

The .env file holds environment variables like API keys or database URLs. This keeps sensitive info out of the code and allows easy changes per environment.

❓ component_behavior

intermediate

What will this Node.js code output when using dotenv?

Given the .env file contains: API_KEY=12345 What does the following code print?

Node.js

import dotenv from 'dotenv';
dotenv.config();
console.log(process.env.API_KEY);

A Error: dotenv not found

B undefined

C 12345

D null

💡 Hint

dotenv loads variables into process.env

dotenv.config() loads variables from .env into process.env. So process.env.API_KEY will be '12345'.

📝 Syntax

advanced

Which option correctly loads environment variables using ES modules in Node.js?

Select the code snippet that correctly imports and configures dotenv in a Node.js ES module.

A

import { config } from 'dotenv';
config();

B

const dotenv = require('dotenv');
dotenv.config();

C require('dotenv').config();

D

import dotenv from 'dotenv';
dotenv.config();

💡 Hint

ES modules use import syntax, not require.

In ES modules, you can import the named export 'config' and call it directly. Option A uses correct ES module syntax.

🔧 Debug

advanced

Why does process.env.MY_VAR return undefined in this Node.js app?

Given .env contains MY_VAR=hello And code is: import dotenv from 'dotenv'; console.log(process.env.MY_VAR); dotenv.config(); Why is the output undefined?

Node.js

import dotenv from 'dotenv';
console.log(process.env.MY_VAR);
dotenv.config();

A process.env variables are only available in CommonJS modules.

B dotenv.config() must be called before accessing process.env variables.

C The .env file is missing from the project root.

D MY_VAR is not a valid environment variable name.

💡 Hint

Think about when dotenv loads the variables.

dotenv.config() loads variables into process.env. If you access process.env before calling config(), variables are not loaded yet.

❓ state_output

expert

What is the output of this Node.js code with multiple dotenv.config calls?

Assuming .env contains VAR=first and .env.local contains VAR=second, What does this code print?

Node.js

import dotenv from 'dotenv';
dotenv.config({ path: '.env' });
dotenv.config({ path: '.env.local' });
console.log(process.env.VAR);

A first

B Error: Multiple dotenv.config calls not allowed

C undefined

D second

💡 Hint

dotenv.config() does not override existing environment variables by default.

dotenv.config() loads variables into process.env but does not overwrite existing keys by default (override: false). The first call sets VAR='first'. The second call finds VAR already set and skips it.