IPC communication between processes in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Node.js IPC example?

Consider the following code where a parent process forks a child process and sends a message. What will the parent log after the child responds?

Node.js

const { fork } = require('child_process');

const child = fork('./child.js');

child.on('message', (msg) => {
  console.log('Parent received:', msg);
});

child.send({ greeting: 'hello' });

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

A Parent received: { reply: 'hello world' }

B No output, process crashes

C Parent received: undefined

D Parent received: { greeting: 'hello' }

💡 Hint

Remember that the child sends back a message with a 'reply' property combining the greeting.

The parent sends { greeting: 'hello' } to the child. The child listens for 'message', then sends back { reply: 'hello world' }. The parent logs this reply.

📝 Syntax

intermediate

Which option correctly sets up IPC message listener in a child process?

You want the child process to listen for messages from the parent. Which code snippet is correct?

A process.onMessage((msg) => { console.log(msg); });

B process.on('message', (msg) => { console.log(msg); });

C process.addListener('msg', (msg) => { console.log(msg); });

D process.listen('message', (msg) => { console.log(msg); });

💡 Hint

Check the exact event name and method to listen for messages on process.

The correct event is 'message' and the method to listen is process.on. Other options use incorrect event names or methods.

🔧 Debug

advanced

Why does this IPC message not arrive in the child process?

Given the parent code below, the child never receives the message. What is the cause?

Node.js

const { fork } = require('child_process');
const child = fork('./child.js');

child.send('start');

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

A The child process must be started with execArgv option

B The message must be an object, not a string

C The child process file path is incorrect or missing

D The parent must wait for 'message' event before sending

💡 Hint

Check if the child process file exists and is correctly referenced.

If the child process file path is wrong, the child never starts properly, so it cannot receive messages.

❓ state_output

advanced

What is the final value of count after IPC messages?

A parent sends increment commands to a child process which updates a count. What is the child's count after these messages?

Node.js

const { fork } = require('child_process');
const child = fork('./counter.js');

child.send({ cmd: 'inc' });
child.send({ cmd: 'inc' });
child.send({ cmd: 'dec' });

// counter.js
let count = 0;
process.on('message', (msg) => {
  if (msg.cmd === 'inc') count++;
  else if (msg.cmd === 'dec') count--;
});

setTimeout(() => {
  process.send({ count });
}, 100);

A 0

B 2

C -1

D 1

💡 Hint

Count increments twice then decrements once.

Two increments add 2, one decrement subtracts 1, so final count is 1.

🧠 Conceptual

expert

Which statement about Node.js IPC channels is true?

Choose the correct statement about IPC communication between parent and child processes in Node.js.

A IPC communication uses a built-in channel that serializes messages as JSON

B IPC channels allow sending only strings between processes

C Child processes can send messages only after the parent sends one first

D IPC messages are synchronous and block the event loop until received

💡 Hint

Think about how data is transferred between processes and the format used.

Node.js IPC serializes messages as JSON objects, allowing structured data transfer asynchronously.