process.env for environment variables in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Node.js code using process.env?

Consider this code snippet that reads environment variables using process.env. What will it print?

Node.js

process.env.TEST_VAR = 'hello';
console.log(process.env.TEST_VAR);

A null

B Throws ReferenceError

C undefined

D "hello"

💡 Hint

Remember that process.env stores environment variables as strings.

The code sets process.env.TEST_VAR to the string "hello" and then logs it. So it prints "hello".

❓ Predict Output

intermediate

What happens if you try to access a non-existent environment variable?

What will this code print if process.env.MY_VAR was never set?

Node.js

console.log(process.env.MY_VAR);

A "" (empty string)

B undefined

C null

D Throws ReferenceError

💡 Hint

Think about what process.env returns for missing keys.

If an environment variable is not set, process.env returns undefined.

❓ component_behavior

advanced

How does changing process.env affect running Node.js code?

If you set process.env.NEW_VAR = '123' inside your Node.js program, what happens to this variable?

A It is available only in the current process and can be accessed anywhere in the code.

B It updates the system environment variables permanently.

C It throws an error because environment variables are read-only.

D It is only available inside the function where it was set.

💡 Hint

Think about the scope of process.env in a running Node.js process.

Setting process.env.NEW_VAR changes the environment variable only for the current Node.js process. It is accessible anywhere in that process but does not affect the system environment.

📝 Syntax

advanced

Which option correctly sets an environment variable in Node.js code?

Choose the correct way to set an environment variable named API_KEY to abc123 inside a Node.js script.

A process.env.API_KEY = 'abc123';

B process.env['API_KEY'] = abc123;

C process.env.API_KEY := 'abc123';

D set process.env.API_KEY = 'abc123';

💡 Hint

Remember how to assign values to object properties in JavaScript.

Option A uses correct JavaScript syntax to assign a string value to process.env.API_KEY. Option A misses quotes around the string, C uses invalid operator, and D uses invalid syntax.

🔧 Debug

expert

Why does this code not print the updated environment variable?

Given this code snippet, why does console.log print undefined instead of the expected value?

Node.js

console.log(process.env.MY_VAR);
process.env.MY_VAR = 'test';

A Because process.env is immutable and throws an error when assigned.

B Because environment variables cannot be changed at runtime.

C Because the environment variable is logged before it is set.

D Because the variable name is case-sensitive and should be lowercase.

💡 Hint

Look at the order of the statements.

The code logs process.env.MY_VAR before it is assigned a value, so it prints undefined. The assignment happens after the log.