IPC communication between processes in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a child process using Node.js built-in module.

Node.js

const { [1] } = require('child_process');
const child = [1].fork('child.js');

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

Aspawn

Bfork

Cexec

DexecFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'spawn' instead of 'fork' which does not set up IPC automatically.

Using 'exec' which runs a shell command but doesn't create a Node.js child process.

The 'fork' method is used to create a new Node.js process and establish IPC communication.

2fill in blank

medium

Complete the code to send a message from the parent process to the child process.

Node.js

child.[1]({ text: 'Hello child' });

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

Asend

BpostMessage

Cwrite

Demit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'emit' which is for event emitters but not for IPC message sending.

Using 'write' which is for streams, not IPC messages.

The 'send' method is used to send messages between parent and child processes in Node.js.

3fill in blank

hard

Fix the error in the child process code to receive messages from the parent.

Node.js

process.[1]('message', (msg) => {
  console.log('Received:', msg);
});

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

Alisten

BaddListener

Con

DonMessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'onMessage' which is not a valid method.

Using 'listen' which is not an event listener method.

The 'on' method listens for events, including 'message' events from the parent process.

4fill in blank

hard

Fill both blanks to send a message from child to parent and listen in parent.

Node.js

// In child process
process.[1]({ reply: 'Hi parent' });

// In parent process
child.[2]('message', (msg) => {
  console.log('From child:', msg);
});

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

Asend

Bon

Cemit

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'emit' instead of 'send' for IPC messages.

Using 'write' which is for streams, not IPC.

Child uses 'send' to send messages; parent uses 'on' to listen for 'message' events.

5fill in blank

hard

Fill all three blanks to create a simple IPC communication where parent sends, child replies, and parent listens.

Node.js

// Parent process
const { [1] } = require('child_process');
const child = [1].fork('child.js');
child.[2]({ greeting: 'Hello child' });
child.[3]('message', (msg) => {
  console.log('Child says:', msg);
});

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

Afork

Bsend

Con

Dspawn

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'spawn' instead of 'fork' which does not set up IPC.

Using 'emit' instead of 'send' for sending messages.

Parent uses 'fork' to create child, 'send' to send message, and 'on' to listen for child's reply.

Practice

1. What does IPC stand for in Node.js context and why is it useful?

easy

A. Internet Protocol Communication; it handles network requests.

B. Internal Process Control; it manages process memory usage.

C. Input-Process-Cache; it speeds up data processing.

D. Inter-Process Communication; it allows processes to exchange messages.

Solution

1. Step 1: Understand IPC meaning and its use in Node.js

   IPC means Inter-Process Communication, which is about processes exchanging data. In Node.js, IPC lets parent and child processes send messages to coordinate work.

2. Final Answer:

   Inter-Process Communication; it allows processes to exchange messages. -> Option D

3. Quick Check:

   IPC = Inter-Process Communication [OK]

Hint: IPC means processes talking to each other [OK]

Common Mistakes:

• Confusing IPC with network protocols
• Thinking IPC manages memory or caching
• Mixing up IPC with internal process controls

2. Which Node.js method is used to create a child process that supports IPC?

easy

A. child_process.spawn()

B. child_process.exec()

C. child_process.fork()

D. child_process.execFile()

Solution

1. Step 1: Review child process methods and identify the one enabling IPC

   spawn(), exec(), execFile() create processes but don't enable IPC by default. fork() creates a child process with an IPC channel for message passing.

2. Final Answer:

   child_process.fork() -> Option C

3. Quick Check:

   fork() creates IPC-enabled child process [OK]

Hint: Use fork() for IPC between parent and child [OK]

Common Mistakes:

• Using spawn() or exec() expecting IPC
• Confusing execFile() with fork()
• Not knowing fork() creates a special IPC channel

3. What will the following code output?

const { fork } = require('child_process');
const child = fork('child.js');
child.on('message', msg => console.log('Parent got:', msg));
child.send('Hello');

// child.js content:
process.on('message', msg => {
  process.send(msg + ' World');
});

medium

A. Parent got: World

B. Parent got: Hello World

C. No output, error occurs

D. Parent got: Hello

Solution

1. Step 1: Trace the message flow and parent's message handler

   The parent sends 'Hello' to child; child appends ' World' and sends back. Parent logs 'Parent got:' plus the message received from child.

2. Final Answer:

   Parent got: Hello World -> Option B

3. Quick Check:

   Child appends ' World' and parent logs it [OK]

Hint: Child appends ' World' before sending back [OK]

Common Mistakes:

• Expecting parent to log original 'Hello' only
• Thinking child does not send a message back
• Confusing message event direction

4. Identify the error in this IPC code snippet:

const { fork } = require('child_process');
const child = fork('child.js');
child.send('Start');
child.on('message', msg => console.log(msg));

// child.js
process.send('Ready');
process.on('message', msg => console.log('Child got:', msg));

medium

A. Parent sends message before child process is ready to receive.

B. Child process sends message before 'message' event listener is set.

C. Child process calls process.send() before parent listens.

D. No error; code works correctly.

Solution

1. Step 1: Analyze message timing and understand child readiness

   Parent sends 'Start' immediately after fork; child may not be ready yet. Child sends 'Ready' immediately but parent may miss it if not listening yet.

2. Final Answer:

   Parent sends message before child process is ready to receive. -> Option A

3. Quick Check:

   Parent must wait for child's 'Ready' before sending [OK]

Hint: Wait for child's ready message before sending [OK]

Common Mistakes:

• Assuming child is ready immediately after fork
• Ignoring asynchronous nature of IPC
• Thinking process.send() order causes error

5. You want to create a Node.js parent process that forks two child processes. Each child sends a number to the parent, and the parent must send back the sum of both numbers to each child. Which approach correctly implements this IPC communication?

hard

A. Parent listens to both children messages, sums numbers, then sends sum to each child using child.send(sum).

B. Each child sends its number to the other child directly using process.send().

C. Parent forks children but does not set up message listeners; children communicate directly.

D. Children send numbers to parent, but parent sends sum only to the first child.

Solution

1. Step 1: Understand parent-child communication and message handling

   Children cannot send messages directly to each other; parent mediates IPC. Parent listens to messages from both children, calculates sum, then sends sum back to each child.

2. Final Answer:

   Parent listens to both children messages, sums numbers, then sends sum to each child using child.send(sum). -> Option A

3. Quick Check:

   Parent mediates and broadcasts sum to children [OK]

Hint: Parent must mediate messages and send sum to all children [OK]

Common Mistakes:

• Trying to send messages directly between children
• Not sending sum to both children
• Not listening to both children's messages in parent