Running JavaScript using Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Node.js script

What is the output when running this Node.js script?

Javascript

console.log('Hello from Node.js!');

A ReferenceError

B undefined

C SyntaxError

D Hello from Node.js!

💡 Hint

Look at what console.log prints to the terminal.

console.log prints the string to the console, so the output is exactly the string inside the quotes.

❓ Predict Output

intermediate

Understanding asynchronous behavior in Node.js

What will be the output order when running this Node.js code?

Javascript

console.log('Start');
setTimeout(() => console.log('Timeout'), 0);
console.log('End');

A

End
Start
Timeout

B

Start
End
Timeout

C

Timeout
Start
End

D

Start
Timeout
End

💡 Hint

setTimeout with 0 delay runs after the current call stack is empty.

The synchronous logs run first: 'Start' then 'End'. The setTimeout callback runs last.

❓ Predict Output

advanced

Output of a Node.js script using process.argv

What will be the output if you run this script with: node script.js hello world?

Javascript

console.log(process.argv.slice(2));

A ["hello", "world"]

B ["node", "script.js", "hello", "world"]

C SyntaxError

D undefined

💡 Hint

process.argv contains command line arguments; slice(2) skips the first two.

process.argv is an array of command line arguments. The first two are node executable and script path.

❓ Predict Output

advanced

Error type when requiring a non-existent module

What error will Node.js throw when running this code?

Javascript

require('nonexistent-module');

A Error: Cannot find module 'nonexistent-module'

B ReferenceError: require is not defined

C TypeError: require is not a function

D SyntaxError: Unexpected token

💡 Hint

Node.js throws an error if a required module is missing.

The error message clearly states the module cannot be found.

❓ Predict Output

expert

Output of a Node.js script using top-level await

What will this script output when run with Node.js 20+?

Javascript

const wait = ms => new Promise(resolve => setTimeout(resolve, ms));

await wait(100);
console.log('Done waiting');

A ReferenceError: wait is not defined

B SyntaxError: await is only valid in async function

C Done waiting

D TypeError: wait is not a function

💡 Hint

Node.js 20+ supports top-level await in modules.

Top-level await pauses execution until the promise resolves, then logs the message.

Practice

1. What does the command node filename.js do?

easy

A. Runs the JavaScript code inside filename.js using Node.js

B. Opens the file filename.js in a text editor

C. Compiles filename.js into a different programming language

D. Deletes the file filename.js from your computer

Solution

1. Step 1: Understand the command node filename.js

   This command tells Node.js to run the JavaScript code inside the file named filename.js.

2. Step 2: Identify what Node.js does

   Node.js executes JavaScript code outside the browser, so it runs the code in the file.

3. Final Answer:

   Runs the JavaScript code inside filename.js using Node.js -> Option A

4. Quick Check:

   node filename.js runs code = C [OK]

Hint: Node runs JavaScript files given after the command [OK]

Common Mistakes:

• Thinking it opens the file in an editor
• Confusing running with compiling
• Assuming it deletes the file

2. Which of the following is the correct way to start an interactive Node.js session in the terminal?

easy

A. run node

B. node filename.js

C. node

D. start node.js

Solution

1. Step 1: Recall how to start Node.js interactively

   Typing node alone in the terminal starts an interactive JavaScript session.

2. Step 2: Check other options

   node filename.js runs a file, not interactive mode; run node and start node.js are invalid commands.

3. Final Answer:

   node -> Option C

4. Quick Check:

   Just node starts interactive mode [OK]

Hint: Just type 'node' to enter interactive mode [OK]

Common Mistakes:

• Adding extra words like 'run' or 'start'
• Confusing running a file with interactive mode
• Using file names when none are needed

3. What will be the output when running this file with node test.js?

console.log('Hello from Node.js!');

medium

A. SyntaxError

B. Hello from Node.js!

C. undefined

D. No output

Solution

1. Step 1: Understand the code inside test.js

   The code uses console.log to print a string to the console.

2. Step 2: Know what Node.js does when running the file

   Node.js executes the code and prints the string to the terminal.

3. Final Answer:

   Hello from Node.js! -> Option B

4. Quick Check:

   console.log prints text = Hello from Node.js! [OK]

Hint: console.log prints output to terminal [OK]

Common Mistakes:

• Expecting no output
• Confusing console.log with return value
• Thinking it causes an error

4. You try to run node app.js but get an error: SyntaxError: Unexpected token. What is the most likely cause?

medium

A. You typed node incorrectly

B. You forgot to save app.js before running

C. Node.js is not installed on your computer

D. The app.js file has invalid JavaScript syntax

Solution

1. Step 1: Understand the error message

   A SyntaxError: Unexpected token means the JavaScript code has a syntax mistake.

2. Step 2: Check other options

   Typing node wrong usually gives a different error; missing Node.js causes 'command not found'; unsaved file won't run but usually no syntax error.

3. Final Answer:

   The app.js file has invalid JavaScript syntax -> Option D

4. Quick Check:

   SyntaxError means code syntax is wrong [OK]

Hint: SyntaxError means code inside file is wrong [OK]

Common Mistakes:

• Assuming Node.js is missing
• Thinking the command was typed wrong
• Not saving file before running

5. You want to quickly test a small JavaScript expression without creating a file. What is the best way to do this using Node.js?

hard

A. Run node in terminal to open interactive mode and type the expression

B. Create a file, write the code, then run node filename.js

C. Use npm start to run the expression

D. Open a browser and run the code in the console

Solution

1. Step 1: Identify how to run code without a file

   Running node alone opens an interactive session where you can type JavaScript directly.

2. Step 2: Compare other options

   Creating a file is slower; npm start runs scripts defined in package.json, not quick tests; browser console is outside Node.js environment.

3. Final Answer:

   Run node in terminal to open interactive mode and type the expression -> Option A

4. Quick Check:

   Interactive mode = quick testing [OK]

Hint: Use just 'node' to test code quickly without files [OK]

Common Mistakes:

• Thinking npm start runs any code
• Believing browser console is Node.js
• Always creating files for small tests