Single-threaded non-blocking I/O concept in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read a file asynchronously using Node.js.

Node.js

const fs = require('fs');
fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) throw err;
  console.log(data);
});
console.log('Reading file...');
// This is non-blocking because [1]

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

AreadFile blocks the thread

Bconsole.log waits for readFile

CreadFile is synchronous

DreadFile runs asynchronously

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking readFile is synchronous and blocks execution

Assuming console.log waits for readFile to finish

The readFile function runs asynchronously, so the program does not wait for it to finish before moving on. This is why the console logs 'Reading file...' first.

2fill in blank

medium

Complete the code to create a simple HTTP server that handles requests without blocking.

Node.js

const http = require('http');
const server = http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World');
});
server.listen(3000);
console.log('Server running at http://localhost:3000/');
// This server is non-blocking because it uses [1]

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

Awhile(true) loops

Bsynchronous file reads

Casynchronous callbacks

Dblocking loops

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking the server blocks while waiting for requests

Confusing synchronous and asynchronous code

The server uses asynchronous callbacks to handle requests, so it does not block the main thread while waiting for requests.

3fill in blank

hard

Fix the error in the code to correctly use non-blocking I/O for reading a file.

Node.js

const fs = require('fs');
const data = fs.readFileSync('data.txt', 'utf8');
console.log(data);
console.log('File read complete');
// To make this non-blocking, replace readFileSync with [1]

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

AreadFile

BreadFileSync

CwriteFileSync

DwriteFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using readFileSync which blocks execution

Confusing readFile and writeFile functions

readFileSync blocks the thread until the file is read. Using readFile makes the operation asynchronous and non-blocking.

4fill in blank

hard

Fill both blanks to create a non-blocking timer that logs a message after 2 seconds.

Node.js

console.log('Start');
setTimeout(() => {
  console.log([1]);
}, [2]);
console.log('End');

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

A'Timer done'

B2000

C1000

D'Done'

Attempts:

3 left

💡 Hint

Common Mistakes

Using synchronous delay instead of setTimeout

Setting the wrong delay time

The setTimeout function schedules the callback to run after 2000 milliseconds (2 seconds) without blocking the main thread.

5fill in blank

hard

Fill all three blanks to create a Promise that resolves after 1 second and logs the result.

Node.js

const wait = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve([1]);
  }, [2]);
});
wait.then((message) => {
  console.log([3]);
});

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

A'Success'

B1000

Cmessage

D'Done'

Attempts:

3 left

💡 Hint

Common Mistakes

Not resolving the Promise with a value

Logging a string instead of the resolved message variable

The Promise resolves with the message 'Success' after 1000 milliseconds. The then method receives the message and logs it.