Chrome DevTools for Node.js in Node.js - Mini Project: Build & Apply

Chrome DevTools for Node.js

📖 Scenario: You are building a simple Node.js script that calculates the sum of numbers in an array. You want to learn how to use Chrome DevTools to debug your Node.js code step-by-step.

🎯 Goal: Create a Node.js script with an array of numbers, a variable to hold the sum, a loop to add the numbers, and a final statement to export the sum. This setup will help you practice debugging with Chrome DevTools.

📋 What You'll Learn

Create an array called numbers with the values [10, 20, 30, 40, 50].

Create a variable called total and set it to 0.

Use a for loop with the variable num to iterate over numbers and add each num to total.

Export the total variable using module.exports.

💡 Why This Matters

🌍 Real World

Developers often need to debug Node.js applications to find and fix bugs. Using Chrome DevTools helps inspect code behavior step-by-step.

💼 Career

Knowing how to debug Node.js code with Chrome DevTools is a valuable skill for backend developers and full-stack engineers working with JavaScript.

1

Create the numbers array

Create an array called numbers with these exact values: [10, 20, 30, 40, 50].

Node.js

// Create an array called numbers with the values [10, 20, 30, 40, 50]
// Your code here

Hint

Use const numbers = [10, 20, 30, 40, 50]; to create the array.

2

Create the total variable

Create a variable called total and set it to 0.

Node.js

const numbers = [10, 20, 30, 40, 50];
// Create a variable called total and set it to 0
// Your code here

Hint

Use let total = 0; to create the variable.

3

Add numbers using a for loop

Use a for loop with the variable num to iterate over numbers and add each num to total.

Node.js

const numbers = [10, 20, 30, 40, 50];
let total = 0;
// Use a for loop with num to add each number to total
// Your code here

Hint

Use for (const num of numbers) { total += num; } to add all numbers.

4

Export the total variable

Export the total variable using module.exports.

Node.js

const numbers = [10, 20, 30, 40, 50];
let total = 0;
for (const num of numbers) {
    total += num;
}
// Export the total variable
// Your code here

Hint

Use module.exports = total; to export the value.

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