Node.js built-in debugger in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How to start the Node.js built-in debugger?

Which command correctly starts the Node.js built-in debugger for a script named app.js?

A node --inspect app.js

B node --debug-brk app.js

C node debug app.js

D node --inspect-brk app.js

💡 Hint

Think about the original command to launch the built-in CLI debugger.

The node debug app.js command starts the built-in CLI debugger in Node.js. The other options relate to the newer inspector protocol or break on start.

❓ component_behavior

intermediate

What happens when you use debugger; in Node.js code?

If you run a Node.js script with the built-in debugger and the code contains a debugger; statement, what will happen when execution reaches that line?

Node.js

console.log('Start');
debugger;
console.log('End');

A The <code>debugger;</code> line is ignored and execution continues immediately.

B Execution pauses and waits for debugger commands before continuing.

C The script throws a syntax error and stops.

D Execution skips the <code>debugger;</code> line and logs only 'End'.

💡 Hint

Think of debugger; as a breakpoint in the code.

The debugger; statement causes Node.js to pause execution when running under the debugger, allowing inspection and commands before continuing.

📝 Syntax

advanced

Identify the correct command to start Node.js debugger and break on first line

Which command starts the Node.js built-in debugger and pauses execution on the first line of server.js?

A node debug --brk server.js

B node debug --break server.js

C node debug server.js --break

D node --inspect server.js

💡 Hint

Look for the correct flag to break on the first line with the built-in debugger.

The --brk flag tells the debugger to break on the first line. It must come before the script name.

🔧 Debug

advanced

What error occurs if you run node debug without a script?

What error message or behavior occurs when you run node debug without specifying a script file?

A Error: No script specified. Usage: node debug <script.js>

B SyntaxError: Unexpected end of input

C The debugger starts but immediately exits with no message.

D ReferenceError: script is not defined

💡 Hint

Think about what the debugger expects as input.

The built-in debugger requires a script file to debug. Running without one shows a usage error.

❓ state_output

expert

What is the output of this Node.js debugger session?

Given the code below and running node debug test.js, what is the output after typing repl and then x + y in the debugger?

Node.js

const x = 5;
const y = 10;
debugger;
console.log(x + y);

A ReferenceError: x is not defined

B SyntaxError: Unexpected identifier

C undefined

D 15

💡 Hint

Variables declared before the debugger statement are accessible in the REPL.

When paused at debugger;, the REPL can access variables in scope. x + y evaluates to 15.