Chrome DevTools for Node.js in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Chrome DevTools for Node.js?

Chrome DevTools for Node.js is a set of debugging tools built into the Chrome browser that lets you inspect, debug, and profile Node.js applications in a visual and interactive way.

beginner

How do you start a Node.js app with Chrome DevTools debugging enabled?

You start your Node.js app with the command: node --inspect your-app.js. This opens a debugging port that Chrome DevTools can connect to.

intermediate

What is the purpose of the --inspect-brk flag in Node.js?

The --inspect-brk flag starts the Node.js app in debug mode and pauses execution on the first line, letting you set breakpoints before any code runs.

intermediate

Name two key features of Chrome DevTools when debugging Node.js apps.

1. Setting breakpoints to pause code execution.
2. Inspecting variables and call stacks to understand program state.
3. Profiling performance to find slow parts.
4. Watching asynchronous operations.

beginner

How can you open Chrome DevTools to debug a Node.js app after starting it with --inspect?

Open Chrome and go to chrome://inspect. Under 'Remote Target', find your Node.js process and click 'inspect' to open DevTools connected to your app.

Which command starts a Node.js app with debugging enabled for Chrome DevTools?

A node --inspect app.js

B node --debug app.js

C node --run-debug app.js

D node --chrome-debug app.js

The correct flag to enable debugging with Chrome DevTools is --inspect.

What does the --inspect-brk flag do?

A Enables debugging but does not pause execution

B Runs the app without debugging

C Starts the app and pauses on the first line for debugging

D Disables debugging

The --inspect-brk flag pauses execution on the first line, letting you set breakpoints before code runs.

Where do you go in Chrome to connect DevTools to a running Node.js process?

A chrome://devtools

B chrome://debugger

C chrome://node-debug

D chrome://inspect

The URL chrome://inspect shows remote targets including Node.js processes for debugging.

Which of these is NOT a feature of Chrome DevTools for Node.js?

A Running SQL queries

B Inspecting variables

C Setting breakpoints

D Profiling performance

Running SQL queries is not a feature of Chrome DevTools; it focuses on debugging and profiling code.

What must you do before Chrome DevTools can debug your Node.js app?

A Install a Chrome extension

B Start Node.js with --inspect flag

C Run Node.js in production mode

D Use a special debugger app

You must start Node.js with the --inspect flag to open the debugging port for DevTools.

Explain how to set up and use Chrome DevTools to debug a Node.js application.

Think about the command line and browser steps.

Describe the benefits of using Chrome DevTools for debugging Node.js apps compared to console.log debugging.

Consider how interactive tools help over just printing messages.

Practice

1. What is the main purpose of using Chrome DevTools with Node.js?

easy

A. To convert Node.js code to browser JavaScript

B. To write Node.js code faster

C. To deploy Node.js apps to the cloud

D. To pause and inspect Node.js code while it runs

Solution

1. Step 1: Understand Chrome DevTools role

   Chrome DevTools is a tool to debug and inspect running code visually.

2. Step 2: Connect to Node.js debugging

   Using DevTools with Node.js lets you pause and inspect your code during execution.

3. Final Answer:

   To pause and inspect Node.js code while it runs -> Option D

4. Quick Check:

   Debugging = Pause and inspect code [OK]

Hint: DevTools helps you pause and check code live [OK]

Common Mistakes:

• Thinking DevTools is for writing code
• Confusing debugging with deployment
• Assuming DevTools converts code formats

2. Which command correctly starts a Node.js app with debugging enabled for Chrome DevTools?

easy

A. node --inspect app.js

B. node app.js --inspect

C. node app.js --debug

D. node debug app.js

Solution

1. Step 1: Recall correct flag usage

   The debugging flag must come before the script name in the command.

2. Step 2: Check each option

   node --inspect app.js uses 'node --inspect app.js' which is the correct syntax to enable debugging.

3. Final Answer:

   node --inspect app.js -> Option A

4. Quick Check:

   Flag before script = correct syntax [OK]

Hint: Put --inspect before your script name [OK]

Common Mistakes:

• Placing --inspect after the script name
• Using deprecated --debug flag
• Typing 'node debug' which is not a valid command

3. Given this command: node --inspect-brk app.js, what happens when you run it?

medium

A. The app crashes immediately

B. The app runs normally without pausing

C. The app pauses on the first line waiting for debugger

D. The app runs but debugging is disabled

Solution

1. Step 1: Understand --inspect-brk flag

   This flag tells Node.js to start debugging and pause before executing any code.

2. Step 2: Predict behavior on running

   The app will wait for a debugger to connect before running the first line.

3. Final Answer:

   The app pauses on the first line waiting for debugger -> Option C

4. Quick Check:

   --inspect-brk = pause at start [OK]

Hint: --inspect-brk pauses app before first line [OK]

Common Mistakes:

• Thinking app runs immediately
• Confusing --inspect with --inspect-brk
• Assuming app crashes on this flag

4. You run node --inspect app.js but Chrome DevTools does not connect. What is a likely cause?

medium

A. You forgot to open chrome://inspect in Chrome

B. You used --inspect-brk instead of --inspect

C. Your Node.js version is too new

D. You ran the command without node

Solution

1. Step 1: Check connection setup

   To debug, you must open Chrome's chrome://inspect page to connect to Node.js.

2. Step 2: Analyze other options

   Using --inspect-brk is valid and pauses app; Node.js version too new is unlikely cause; running without node would cause error.

3. Final Answer:

   You forgot to open chrome://inspect in Chrome -> Option A

4. Quick Check:

   Open chrome://inspect to connect debugger [OK]

Hint: Always open chrome://inspect to connect debugger [OK]

Common Mistakes:

• Assuming --inspect-brk is required
• Ignoring the need to open Chrome inspect page
• Not running with 'node' command

5. You want to debug a Node.js app that crashes immediately on start. You run node --inspect app.js and connect Chrome DevTools but can't find where it crashes. What should you do to catch the crash at the start?

hard

A. Add debugger; inside app.js after the crash line

B. Run with node --inspect-brk app.js to pause before code runs

C. Run node --inspect app.js with extra logging

D. Use node debug app.js instead

Solution

1. Step 1: Understand crash timing

   If the app crashes immediately, you need to pause before any code runs to inspect it.

2. Step 2: Use correct flag to pause early

   The --inspect-brk flag pauses execution on the first line, letting you catch early crashes.

3. Step 3: Evaluate other options

   Adding debugger; after crash won't help if crash happens before it; extra logging may miss early crash; node debug is outdated.

4. Final Answer:

   Run with node --inspect-brk app.js to pause before code runs -> Option B

5. Quick Check:

   --inspect-brk pauses early to catch crashes [OK]

Hint: Use --inspect-brk to pause before app starts [OK]

Common Mistakes:

• Placing debugger after crash point
• Relying only on logs for early crashes
• Using deprecated debug command