Reading data with Readable streams in Node.js - Mini Project: Build & Apply

Reading data with Readable streams

📖 Scenario: You are building a simple Node.js program that reads data from a file using a Readable stream. This is useful when working with large files or data sources that send data in chunks.

🎯 Goal: Learn how to create a Readable stream from a file, set up a data event listener to read chunks, and handle the end of the stream.

📋 What You'll Learn

Create a Readable stream from a file named example.txt

Set a variable to count the total bytes read

Use the data event to add chunk sizes to the total bytes

Use the end event to mark the completion of reading

💡 Why This Matters

🌍 Real World

Reading large files or data streams in chunks helps avoid loading everything into memory at once, which is important for performance and scalability.

💼 Career

Understanding streams is essential for backend developers working with file systems, network data, or any large data processing in Node.js.

1

Create a Readable stream from a file

Write code to import the fs module and create a Readable stream called readStream from the file example.txt using fs.createReadStream.

Node.js

const fs = require('fs');
// Your code here

Need a hint?

Use require('fs') to import the file system module. Then use fs.createReadStream('example.txt') to create the stream.

2

Set up a variable to count bytes

Add a variable called totalBytes and set it to 0. This will keep track of how many bytes have been read from the stream.

Node.js

const fs = require('fs');
const readStream = fs.createReadStream('example.txt');
// Your code here

Need a hint?

Use let totalBytes = 0; to create the counter variable.

3

Add a data event listener to count bytes

Use readStream.on('data', chunk => { ... }) to listen for data chunks. Inside the callback, add chunk.length to totalBytes.

Node.js

const fs = require('fs');
const readStream = fs.createReadStream('example.txt');
let totalBytes = 0;
// Your code here

Need a hint?

Use the data event to get chunks and add their length to totalBytes.

4

Add an end event listener to finish reading

Add a listener for the end event on readStream using readStream.on('end', () => { ... }). Inside, add a comment // Reading finished to mark the end of the stream.

Node.js

const fs = require('fs');
const readStream = fs.createReadStream('example.txt');
let totalBytes = 0;
readStream.on('data', chunk => {
    totalBytes += chunk.length;
});
// Your code here

Need a hint?

Use the end event to know when the stream has finished sending data.