Long polling as fallback in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple HTTP server in Node.js.

Node.js

const http = require('http');
const server = http.createServer((req, res) => {
  res.end('Hello World');
});
server.listen([1]);

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

Ahttp

B3000

Clocalhost

Dserver

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string like 'http' instead of a port number.

Passing the server object instead of a port.

The server.listen method requires a port number to start the server. 3000 is a common choice.

2fill in blank

medium

Complete the code to set the response header for JSON content.

Node.js

res.writeHead(200, { 'Content-Type': [1] });

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

A'application/json'

B'text/html'

C'text/plain'

D'image/png'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text/html' when sending JSON data.

Forgetting to set the Content-Type header.

For JSON responses, the Content-Type header should be 'application/json'.

3fill in blank

hard

Fix the error in the long polling function to correctly send a response when data is ready.

Node.js

function longPoll(req, res) {
  if (dataReady) {
    res.[1](JSON.stringify({ message: 'Data ready' }));
  } else {
    // wait and retry
  }
}

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

AwriteHead

Bwrite

Csend

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.write() without ending the response.

Using res.send() which is not a native Node.js method.

The res.end() method sends the response and closes the connection, which is needed here.

4fill in blank

hard

Fill both blanks to correctly implement a long polling retry with a timeout.

Node.js

function longPoll(req, res) {
  if (dataReady) {
    res.end(JSON.stringify({ data: 'Here is your data' }));
  } else {
    setTimeout(() => {
      [1](req, res);
    }, [2]);
  }
}

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

AlongPoll

BsendData

C5000

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a wrong function name.

Using too long or too short timeout values.

The function calls itself after 1000 milliseconds (1 second) to retry the long polling.

5fill in blank

hard

Fill all three blanks to create a fallback long polling server that responds with JSON data.

Node.js

const http = require('http');
let dataReady = false;

const server = http.createServer((req, res) => {
  if (req.url === '/poll') {
    res.writeHead(200, { 'Content-Type': [1] });
    if (dataReady) {
      res.[2](JSON.stringify({ status: 'ready' }));
      dataReady = false;
    } else {
      setTimeout(() => {
        res.[3](JSON.stringify({ status: 'timeout' }));
      }, 3000);
    }
  } else {
    res.writeHead(404);
    res.end();
  }
});

server.listen(8080);

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

A'application/json'

Bend

Cwrite

D'text/plain'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text/plain' instead of 'application/json' for JSON data.

Using res.write() without ending the response.

The server sets the JSON content type and uses res.end() to send and close the response in both cases.