WebSocket basics — incoming and outgoing messages

Pattern

A WebSocket is a two-way channel. Subscribe means "listen to the server". next on the socket means "send to the server". Not to be confused with HTTP, where request/response is strictly one-to-one.

The problem it solves

The callback API socket.on('message', ...) and socket.send(...) sprawls across component handlers, cleans up poorly on destroy, and easily leaves a "zombie listener" after you leave the page.

Operators and why they matter

• Subject simulates the duplex channel: subscribe for incoming, next for outgoing.
• In reality, use webSocket from rxjs/webSocket — it gives exactly this model with socket.next(command).

Gotchas

• HTTP completes on its own; a WebSocket doesn't. It can live for hours and needs explicit teardown and reconnect.
• Don't create a new socket on every subscribe in a component. One socket in a singleton service; components subscribe to derived streams.
• You can't swallow socket errors. You need either a reconnect or an explicit offline state in the UI.