Reading data with Readable streams in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Node.js Readable stream code?

Consider the following code that reads data from a Readable stream. What will be logged to the console?

Node.js

import { Readable } from 'stream';

const readable = Readable.from(['Hello', ' ', 'World']);

readable.on('data', chunk => {
  console.log(chunk.toString());
});

A Hello\n \nWorld\n

B Hello World (all in one chunk)

C Hello World\n

D Hello World

💡 Hint

Think about how the 'data' event emits chunks separately.

The Readable stream emits each chunk separately on the 'data' event. Each chunk is logged on its own line, so the console shows each piece on a new line.

📝 Syntax

intermediate

Which option correctly creates a Readable stream from an array of strings?

You want to create a Readable stream from an array of strings ['a', 'b', 'c']. Which code snippet is correct?

A const readable = Readable(['a', 'b', 'c']);

B const readable = new Readable(['a', 'b', 'c']);

C const readable = new Readable.from(['a', 'b', 'c']);

D const readable = Readable.from(['a', 'b', 'c']);

💡 Hint

Check the correct way to use Readable.from static method.

Readable.from is a static method to create a stream from iterable data. It is called directly on Readable, not with new.

❓ state_output

advanced

What is the value of 'dataCollected' after this code runs?

This code reads data from a Readable stream and collects it into a string. What is the final value of 'dataCollected'?

Node.js

import { Readable } from 'stream';

const readable = Readable.from(['Node', 'JS']);

let dataCollected = '';

readable.on('data', chunk => {
  dataCollected += chunk.toString();
});

readable.on('end', () => {
  // end event
});

A "NodeJS"

B "Node JS"

C "Node\nJS"

D "Node"

💡 Hint

Remember how the chunks are emitted and concatenated.

The stream emits 'Node' and then 'JS' as chunks. Concatenating them results in 'NodeJS'.

🔧 Debug

advanced

Why does this Readable stream code cause a runtime error?

Examine the code below. Why does it throw an error when run?

Node.js

import { Readable } from 'stream';

const readable = new Readable({
  read() {
    this.push('data');
    this.push(null);
  }
});

readable.on('data', chunk => {
  console.log(chunk.toString());
});

readable.on('end', () => {
  console.log('Stream ended');
});

A Calling readable.read() manually causes error because data is pushed asynchronously.

B No error occurs; the code runs and logs 'data' and 'Stream ended'.

C The stream emits data twice causing a conflict.

D The read() method pushes data but calling readable.read() is incorrect usage causing error.

💡 Hint

Consider how the Readable stream's read() method is used internally.

Calling readable.read() manually when the stream is in flowing mode and pushing data inside read() causes an error because read() is meant to be called by the stream internally.

🧠 Conceptual

expert

Which option best explains how backpressure is handled in Node.js Readable streams?

Backpressure helps control data flow in streams. Which explanation correctly describes how Node.js Readable streams handle backpressure?

A Backpressure is not handled by Readable streams; it must be managed manually by the developer.

B The stream drops data chunks if the consumer is slow to avoid memory overflow.

C The stream buffers data internally and pauses emitting 'data' events when the consumer is slow, resuming when ready.

D The stream automatically speeds up the producer to match the consumer's speed.

💡 Hint

Think about how streams avoid overwhelming the consumer.

Node.js Readable streams manage backpressure by buffering data and pausing the flow of 'data' events when the consumer cannot keep up, then resuming when ready.