Debugging with VS Code in Node.js - Practice Questions

Challenge - 5 Problems

🔧 Debug

intermediate

Identify the cause of the breakpoint not hitting

You set a breakpoint in VS Code on line 5 of your Node.js file, but when you run the debugger, it never pauses there. What is the most likely reason?

Node.js

console.log('Start');
function greet() {
  console.log('Hello');
}
greet();
console.log('End');

A The code has a syntax error before line 5.

B The file is not saved before starting the debugger.

C The breakpoint is set on a comment line.

D The debugger is not attached to the running process.

💡 Hint

Check if the debugger is connected to the right process.

If the debugger is not attached, breakpoints won't be hit. Setting breakpoints on comments or unsaved files won't cause this issue. Syntax errors usually prevent the program from running.

❓ component_behavior

intermediate

What happens when you use 'console.log' inside a VS Code debug session?

During a Node.js debug session in VS Code, you add console.log statements inside your code. Where will the output appear?

Node.js

console.log('Debugging output');

A In the Terminal panel of VS Code.

B In the Debug Console panel of VS Code.

C In a popup alert window.

D In the Problems panel of VS Code.

💡 Hint

Think about where debug output usually shows in VS Code.

Console.log output during debugging appears in the Debug Console, not the Terminal or Problems panel.

📝 Syntax

advanced

Which launch.json configuration correctly starts a Node.js debug session?

You want to debug a Node.js file named app.js using VS Code. Which launch.json snippet will correctly launch the debugger?

A { "type": "node", "request": "launch", "name": "Launch Program", "program": "${workspaceFolder}/app.js" }

B { "type": "node", "request": "attach", "name": "Attach to Program", "program": "app.js" }

C { "type": "node", "request": "launch", "name": "Start Debug", "file": "app.js" }

D { "type": "node", "request": "start", "name": "Run Debug", "program": "app.js" }

💡 Hint

Check the correct keys for launch configuration.

The 'launch' request with 'program' key pointing to the file is correct. 'attach' is for attaching to running processes. 'file' and 'start' are invalid keys.

❓ state_output

advanced

What is the value of 'count' when the debugger pauses at the breakpoint?

Consider this Node.js code with a breakpoint on line 6. What is the value of 'count' when paused there?

Node.js

let count = 0;
for(let i = 0; i < 3; i++) {
  count += i;
  debugger;
}
console.log(count);

A 1

B 0

C 6

D 3

💡 Hint

The breakpoint on line 6 is after the loop; calculate the final value of count.

The loop iterates three times (i=0: count=0; i=1: count=1; i=2: count=3). The breakpoint is on line 6 after the loop completes, so count=3. The 'debugger;' statements cause pauses inside the loop, but the breakpoint on line 6 is hit after continuing past them.

🧠 Conceptual

expert

Why use 'sourceMaps' in VS Code debugging for Node.js?

You are debugging a Node.js app written in TypeScript using VS Code. Why is setting "sourceMaps": true in launch.json important?

A It allows the debugger to map the compiled JavaScript back to the original TypeScript source code.

B It speeds up the debugging process by skipping source files.

C It enables debugging of external libraries automatically.

D It disables breakpoints in JavaScript files.

💡 Hint

Think about how TypeScript compiles to JavaScript and how debugging works.

Source maps connect the compiled JavaScript to the original TypeScript, letting you debug the original code instead of the compiled output.