Typing indicators debounced at client and expire server-side on timeout

A typing indicator fired on every keystroke with no debounce generates roughly one WebSocket event per 100ms per active user. For a community with 100 simultaneous typists, that is 1,000 events per second — before any real messages are sent. Without server-side expiry, users who close their browser mid-compose are shown as typing indefinitely. Both failure modes inflate bandwidth, CPU cost, and connection noise for zero user-visible benefit, violating ISO 25010 performance-efficiency requirements.

Debounce the client-side typing event to at most one emission per 500 ms, and expire server-side typing state after 10 seconds without an update.

// Client: debounce before emitting
let stopTimer: ReturnType<typeof setTimeout>;
const onInput = () => {
  socket.emit('typing', { channel });
  clearTimeout(stopTimer);
  stopTimer = setTimeout(() => socket.emit('typing_stop', { channel }), 3_000);
};
input.addEventListener('input', onInput);

// Server: expire stale typing status
const typingTimers = new Map<string, ReturnType<typeof setTimeout>>();
socket.on('typing', ({ channel }) => {
  if (typingTimers.has(socket.userId)) clearTimeout(typingTimers.get(socket.userId)!);
  const t = setTimeout(() => {
    removeTypingUser(channel, socket.userId);
    broadcastTypingList(channel);
  }, 10_000);
  typingTimers.set(socket.userId, t);
  addTypingUser(channel, socket.userId);
  broadcastTypingList(channel);
});