03 — Events & Streams

Core Concepts

EventEmitter

• Node's pub/sub pattern — emit events, register listeners
• on(event, fn) — listen for event
• once(event, fn) — listen once then auto-remove
• emit(event, ...args) — fire event with data
• off(event, fn) / removeListener — remove listener

Streams

• Readable — source of data (file read, HTTP request)
• Writable — destination for data (file write, HTTP response)
• Duplex — both readable and writable (TCP socket)
• Transform — modify data as it passes through (compression, encryption)
• pipeline() — connect streams with proper error handling

Why Streams?

• Process data in chunks instead of loading everything into memory
• A 1GB file needs ~1GB RAM without streams, but only ~64KB with streams