Node.js Streams Cheatsheet

Streams are collections of data that might not be available all at once, enabling efficient consumption of large files and network payloads without exhausting memory.

Stream Types Overview

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Pipeline & Modern stream/promises

Modern Node.js provides pipeline to safely link streams with automatic error handling and resource cleanup:

const { pipeline } = require('stream/promises');
const fs = require('fs');
const zlib = require('zlib');

async function compressFile() {
  await pipeline(
    fs.createReadStream('source.tar'),
    zlib.createGzip(),
    fs.createWriteStream('source.tar.gz')
  );
  console.log('Compression complete');
}

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Creating Custom Streams

1. Custom Readable Stream

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

function createTimestampStream() {
  let count = 0;
  return new Readable({
    objectMode: true,
    read() {
      if (count >= 5) {
        this.push(null); // End of stream
      } else {
        this.push({ id: ++count, time: new Date() });
      }
    }
  });
}

2. Custom Transform Stream

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

const uppercaseTransformer = new Transform({
  transform(chunk, encoding, callback) {
    const transformed = chunk.toString().toUpperCase();
    callback(null, transformed);
  }
});

3. Custom Writable Stream

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

const consoleWriter = new Writable({
  objectMode: true,
  write(chunk, encoding, callback) {
    console.log('Writing chunk:', chunk);
    callback();
  }
});

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Flowing vs Paused Mode

Readable streams operate in either paused or flowing mode:

const stream = fs.createReadStream('data.csv');

// Attaching a 'data' listener automatically activates flowing mode
stream.on('data', (chunk) => {
  console.log(`Received ${chunk.length} bytes`);
});

// Explicit flow control
stream.pause();  // Temporarily suspend events
stream.resume(); // Resume streaming events

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Stream Events

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References

• Node.js Stream Documentation
• Stream Handbook by Substack