Node.js — Streams

What are Streams?

Streams are objects for reading/writing data continuously.

Stream Types

Type	Description
Readable	Source of data
Writable	Destination for data
Duplex	Both readable and writable
Transform	Modify data in transit

Readable Stream

const fs = require('fs');

const readable = fs.createReadStream('file.txt', {
    encoding: 'utf8',
    highWaterMark: 16
});

readable.on('data', chunk => {
    console.log(`Received ${chunk.length} bytes`);
});

readable.on('end', () => {
    console.log('No more data');
});

Writable Stream

const writable = fs.createWriteStream('output.txt');

writable.write('Hello, ');
writable.write('World!\n');
writable.end();

Piping Streams

const readable = fs.createReadStream('input.txt');
const writable = fs.createWriteStream('output.txt');

readable.pipe(writable);

Transform Stream

const { Transform } = require('stream');

const upperCase = new Transform({
    transform(chunk, encoding, callback) {
        this.push(chunk.toString().toUpperCase());
        callback();
    }
});

process.stdin.pipe(upperCase).pipe(process.stdout);

Mini Practice

1. Read a file with streams
2. Write to a file with streams
3. Pipe readable to writable
4. Create a transform stream

Up Next

Continue with Buffers — binary data handling.