Node.js built-in debugger in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the Node.js debugger with a script named app.js.

Node.js

node [1] app.js

Drag options to blanks, or click blank then click option'

A--watch

Bdebug

C--inspect

D--run

Attempts:

3 left

💡 Hint

Common Mistakes

Using --inspect instead of debug starts the inspector, not the legacy debugger.

Using --watch or --run are invalid for debugging.

Use debug to start the built-in Node.js debugger in legacy mode.

2fill in blank

medium

Complete the code to start Node.js with the modern debugger listening on port 9229.

Node.js

node [1]=9229 app.js

Drag options to blanks, or click blank then click option'

A--debug

B--trace

C--inspect

D--profile

Attempts:

3 left

💡 Hint

Common Mistakes

Using --debug is deprecated and replaced by --inspect.

Using --trace or --profile does not start the debugger.

The --inspect flag starts the modern debugger and listens on the specified port.

3fill in blank

hard

Fix the error in the code to start the debugger and pause execution on the first line.

Node.js

node --inspect-brk=[1] app.js

Drag options to blanks, or click blank then click option'

A9229

Bdebug

Cstart

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'debug' or 'true' causes an error because the flag expects a port number.

Omitting the port number or using invalid values.

The --inspect-brk flag expects a port number to listen on, such as 9229.

4fill in blank

hard

Fill both blanks to start the Node.js debugger and open the inspector on port 9230.

Node.js

node [1]=[2] app.js

Drag options to blanks, or click blank then click option'

A--inspect

B9229

C9230

D--debug

Attempts:

3 left

💡 Hint

Common Mistakes

Using --debug instead of --inspect starts the legacy debugger.

Using the wrong port number causes connection issues.

Use --inspect=9230 to start the modern debugger listening on port 9230.

5fill in blank

hard

Fill all three blanks to start Node.js with the debugger, pause on the first line, and enable the inspector on port 9240.

Node.js

node [1] [2]=[3] app.js

Drag options to blanks, or click blank then click option'

A--inspect-brk

B--inspect

C9240

D--debug

Attempts:

3 left

💡 Hint

Common Mistakes

Using --debug instead of --inspect for modern debugging.

Not specifying the port or using the wrong flag order.

--inspect-brk pauses on the first line, --inspect=9240 enables the inspector on port 9240.

Practice

1. What is the primary purpose of the Node.js built-in debugger?

easy

A. To pause and inspect code execution to find bugs

B. To speed up the execution of Node.js programs

C. To automatically fix syntax errors in code

D. To deploy Node.js applications to the cloud

Solution

1. Step 1: Understand the debugger's role

   The Node.js built-in debugger allows developers to pause code execution and inspect variables and flow.

2. Step 2: Compare options to debugger purpose

   Only To pause and inspect code execution to find bugs describes pausing and inspecting code to find bugs, which matches the debugger's function.

3. Final Answer:

   To pause and inspect code execution to find bugs -> Option A

4. Quick Check:

   Debugger purpose = pause and inspect [OK]

Hint: Debugger = pause and inspect code to find bugs [OK]

Common Mistakes:

• Thinking debugger speeds up code
• Confusing debugger with auto-fix tools
• Assuming debugger deploys apps

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

easy

A. node debug app.js

B. node run app.js

C. node inspect app.js

D. node start app.js

Solution

1. Step 1: Recall debugger start commands

   The modern way to start the Node.js debugger is using node inspect followed by the script name.

2. Step 2: Check each option

   node inspect app.js uses node inspect app.js, which is correct. node debug app.js uses deprecated node debug. Options B and D are invalid commands.

3. Final Answer:

   node inspect app.js -> Option C

4. Quick Check:

   Start debugger = node inspect [OK]

Hint: Use 'node inspect' to start debugger, not 'node debug' [OK]

Common Mistakes:

• Using 'node debug' which is deprecated
• Using 'node run' or 'node start' which don't start debugger
• Confusing command syntax order

3. Given this code snippet with debugger statements:

function add(a, b) {
  debugger;
  return a + b;
}

console.log(add(2, 3));

What happens when you run node inspect script.js on this file?

medium

A. The program runs without pausing and prints 5 immediately

B. The program crashes with an exception

C. SyntaxError occurs due to debugger statement

D. Execution pauses at the debugger line before returning the sum

Solution

1. Step 1: Understand debugger statement effect

   The debugger; statement causes the debugger to pause execution at that line when running under a debugger.

2. Step 2: Analyze program flow

   Running node inspect pauses at the debugger; line inside add before returning the sum, allowing inspection.

3. Final Answer:

   Execution pauses at the debugger line before returning the sum -> Option D

4. Quick Check:

   Debugger statement pauses execution under debugger [OK]

Hint: Debugger statement pauses code only when debugger runs [OK]

Common Mistakes:

• Thinking debugger statement causes syntax error
• Assuming program runs without pause under debugger
• Confusing debugger statement with console.log

4. You run node inspect app.js but the debugger does not pause at your debugger; statement inside a function. What is a likely cause?

medium

A. The debugger command is misspelled

B. You forgot to save the file after adding the debugger statement

C. Node.js version does not support debugger

D. Debugger statements only work in browser JavaScript

Solution

1. Step 1: Check file changes

   If the file was not saved after adding debugger;, the running code won't include it, so debugger won't pause.

2. Step 2: Evaluate other options

   Debugger command spelling doesn't affect pause at debugger;. Node.js supports debugger in recent versions. Debugger statements work in Node.js, not only browsers.

3. Final Answer:

   You forgot to save the file after adding the debugger statement -> Option B

4. Quick Check:

   Unsaved file = debugger ignored [OK]

Hint: Always save files before debugging to include changes [OK]

Common Mistakes:

• Assuming debugger statements only work in browsers
• Ignoring file save before running debugger
• Blaming Node.js version without checking

5. You want to debug a Node.js script and step through each line inside a loop. Which command should you use after starting node inspect script.js to move to the next line without entering functions?

hard

A. next

B. cont

C. step

D. out

Solution

1. Step 1: Understand debugger commands

   cont continues running until next breakpoint, step enters functions, next moves to next line without entering functions, out steps out of current function.

2. Step 2: Choose command for stepping through loop lines

   To move line by line in the current function (like inside a loop) without entering called functions, next is the correct command.

3. Final Answer:

   next -> Option A

4. Quick Check:

   Step over lines = next [OK]

Hint: Use 'next' to step over lines without entering functions [OK]

Common Mistakes:

• Using 'cont' which runs without pausing
• Using 'step' which enters functions
• Using 'out' which exits current function