Chrome DevTools for Node.js in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Understanding Chrome DevTools Debugger Behavior in Node.js

When you run a Node.js script with the --inspect-brk flag and open Chrome DevTools, what happens immediately after the script starts?

Node.js

node --inspect-brk script.js

A The script runs fully without pausing, and DevTools attaches after completion.

B The script pauses only if a breakpoint is manually set in DevTools after starting.

C The script pauses on the first line before executing any code, waiting for you to resume.

D The script throws an error because <code>--inspect-brk</code> is deprecated.

💡 Hint

Think about what the brk part in --inspect-brk means.

The --inspect-brk flag tells Node.js to start the debugger and pause execution on the first line of the script. This allows you to set breakpoints or inspect variables before any code runs.

📝 Syntax

intermediate

Correct Usage of the Node.js Inspector Protocol URL

Which of the following is the correct format of the WebSocket URL used by Chrome DevTools to connect to a running Node.js process with the inspector enabled?

A ws://127.0.0.1:9229/uuid

B http://127.0.0.1:9229/uuid

C wss://127.0.0.1:9229/uuid

D ftp://127.0.0.1:9229/uuid

💡 Hint

DevTools uses a WebSocket connection, not HTTP or FTP.

The Node.js inspector listens on a WebSocket URL starting with ws:// by default on port 9229. This is how Chrome DevTools communicates with the Node.js process.

🔧 Debug

advanced

Identifying the Cause of a Debugger Connection Failure

You start a Node.js process with node --inspect=localhost:9230 app.js but Chrome DevTools fails to connect. What is the most likely reason?

A The <code>--inspect</code> flag requires the port to be above 1024, and 9230 is invalid.

B The <code>localhost</code> hostname is not allowed; you must use <code>0.0.0.0</code>.

C The Node.js process must be started with <code>--inspect-brk</code> to allow any connection.

D Chrome DevTools only connects to port 9229 by default, so it cannot connect to 9230 without manual configuration.

💡 Hint

Check the default port Chrome DevTools expects for Node.js debugging.

By default, Chrome DevTools connects to port 9229 for Node.js debugging. If you specify a different port like 9230, you must manually tell DevTools to connect to that port. Otherwise, it will fail to connect.

❓ state_output

advanced

Effect of Pausing Execution in Chrome DevTools on Node.js Event Loop

If you pause a running Node.js script in Chrome DevTools, what happens to the Node.js event loop and asynchronous callbacks?

A The event loop continues running, so asynchronous callbacks execute even while paused.

B The event loop is paused, so no asynchronous callbacks or timers run until resumed.

C Only timers pause, but I/O callbacks continue running during the pause.

D The event loop crashes and the Node.js process exits.

💡 Hint

Think about what pausing execution means for the entire JavaScript runtime.

When you pause execution in Chrome DevTools, the entire Node.js event loop is paused. This means no asynchronous callbacks, timers, or I/O events will run until you resume the script.

🧠 Conceptual

expert

Understanding Source Map Support in Node.js Debugging with Chrome DevTools

You are debugging a Node.js application written in TypeScript using Chrome DevTools. You notice that breakpoints in the original TypeScript files are not hit, only in the compiled JavaScript files. What is the most likely cause?

A Source maps are not properly generated or linked, so DevTools cannot map JS back to TS files.

B Chrome DevTools does not support debugging TypeScript files at all.

C You must run Node.js with <code>--inspect-brk</code> to debug TypeScript source maps.

D TypeScript files must be renamed to .js for DevTools to recognize breakpoints.

💡 Hint

Check if the compiled JavaScript includes source map references.

For Chrome DevTools to map breakpoints from JavaScript back to TypeScript, source maps must be generated during compilation and properly linked in the JavaScript files. Without source maps, DevTools only sees the compiled JS.