रीयल-टाइम UI पैटर्न

async function likePost(id) {
  // 1. Optimistically update UI:
  setLikes(l => ({ ...l, [id]: (l[id] || 0) + 1 }));
  setLiked(prev => ({ ...prev, [id]: true }));

  try {
    await fetch(`/api/posts/${id}/like`, { method: 'POST' });
  } catch (err) {
    // 2. Rollback on failure:
    setLikes(l => ({ ...l, [id]: (l[id] || 1) - 1 }));
    setLiked(prev => ({ ...prev, [id]: false }));
    toast.error('Could not like — please retry');
  }
}

async function addComment(text) {
  const tempId = `tmp-${Date.now()}`;
  setComments(c => [...c, { id: tempId, text, pending: true }]);

  try {
    const saved = await fetch('/api/comments', {
      method: 'POST',
      body: JSON.stringify({ text })
    }).then(r => r.json());

    setComments(c => c.map(m => m.id === tempId ? saved : m));
  } catch (err) {
    setComments(c => c.map(m => m.id === tempId ? { ...m, error: true } : m));
  }
}

const queue = JSON.parse(localStorage.getItem('queue') || '[]');

function enqueue(action) {
  queue.push(action);
  localStorage.setItem('queue', JSON.stringify(queue));
  trySend();
}

async function trySend() {
  while (queue.length && navigator.onLine) {
    const action = queue[0];
    try {
      await fetch(action.url, action);
      queue.shift();
      localStorage.setItem('queue', JSON.stringify(queue));
    } catch {
      break; // stop until online
    }
  }
}

window.addEventListener('online', trySend);

function applyServerSnapshot(newList, currentList) {
  const current = new Map(currentList.map(i => [i.id, i]));
  const result = newList.map(item => {
    const prev = current.get(item.id);
    if (!prev) return { ...item, _state: 'new' };
    if (prev.updatedAt !== item.updatedAt) return { ...item, _state: 'updated' };
    return prev;
  });
  return result;
}

// Server sends: { type: 'patch', id: 42, fields: { likes: 11 } }
ws.on('message', (msg) => {
  if (msg.type === 'patch') {
    setPosts(posts => posts.map(p =>
      p.id === msg.id ? { ...p, ...msg.fields } : p
    ));
  }
});

import { throttle } from 'lodash-es';

const applyUpdate = throttle((data) => {
  setData(data);
}, 16); // ~60fps

ws.on('tick', applyUpdate);

ws.on('presence', ({ users }) => {
  setOnlineUsers(users);
});

ws.on('typing', ({ user, isTyping }) => {
  setTypingUsers(t => isTyping
    ? [...t.filter(u => u.id !== user.id), user]
    : t.filter(u => u.id !== user.id));
});

{!isConnected && (
  <div className="connection-banner">
    Reconnecting... Your changes will sync when you're back online.
  </div>
)}