---
name: convex-realtime-0587fc8fc044
description: Realtime subscriptions and optimistic updates in Convex. Use when implementing live data updates, optimistic UI, pagination with realtime, presence indicators, typing indicators, or any feature requiring instant data synchronization.
---

# Convex Realtime

## Automatic Subscriptions

Queries in Convex automatically subscribe to updates:

```typescript
// React component - automatically updates when data changes
function TaskList({ userId }: { userId: Id<"users"> }) {
  const tasks = useQuery(api.tasks.list, { userId });

  if (tasks === undefined) return <Loading />;

  return (
    <ul>
      {tasks.map((task) => (
        <li key={task._id}>{task.title}</li>
      ))}
    </ul>
  );
}
```

## Optimistic Updates

### Basic Optimistic Update

```typescript
import { useMutation } from "convex/react";
import { api } from "../convex/_generated/api";

function AddTask() {
  const addTask = useMutation(api.tasks.create).withOptimisticUpdate(
    (localStore, args) => {
      const { title, userId } = args;

      // Get current tasks from local cache
      const currentTasks = localStore.getQuery(api.tasks.list, { userId });
      if (currentTasks === undefined) return;

      // Add optimistic task
      const optimisticTask = {
        _id: crypto.randomUUID() as Id<"tasks">,
        _creationTime: Date.now(),
        title,
        userId,
        completed: false,
      };

      // Update local cache immediately
      localStore.setQuery(api.tasks.list, { userId }, [
        optimisticTask,
        ...currentTasks,
      ]);
    }
  );

  return (
    <button onClick={() => addTask({ title: "New Task", userId })}>
      Add Task
    </button>
  );
}
```

### Optimistic Delete

```typescript
const deleteTask = useMutation(api.tasks.remove).withOptimisticUpdate(
  (localStore, args) => {
    const { taskId, userId } = args;

    const currentTasks = localStore.getQuery(api.tasks.list, { userId });
    if (currentTasks === undefined) return;

    // Remove task from local cache
    localStore.setQuery(
      api.tasks.list,
      { userId },
      currentTasks.filter((t) => t._id !== taskId)
    );
  }
);
```

### Optimistic Toggle

```typescript
const toggleTask = useMutation(api.tasks.toggle).withOptimisticUpdate(
  (localStore, args) => {
    const { taskId, userId } = args;

    const currentTasks = localStore.getQuery(api.tasks.list, { userId });
    if (currentTasks === undefined) return;

    // Toggle completed status locally
    localStore.setQuery(
      api.tasks.list,
      { userId },
      currentTasks.map((t) =>
        t._id === taskId ? { ...t, completed: !t.completed } : t
      )
    );
  }
);
```

## Paginated Realtime

```typescript
// convex/messages.ts
import { query } from "./_generated/server";
import { v } from "convex/values";
import { paginationOptsValidator } from "convex/server";

export const list = query({
  args: {
    channelId: v.id("channels"),
    paginationOpts: paginationOptsValidator,
  },
  returns: v.object({
    page: v.array(v.object({
      _id: v.id("messages"),
      _creationTime: v.number(),
      content: v.string(),
      authorId: v.id("users"),
    })),
    isDone: v.boolean(),
    continueCursor: v.string(),
  }),
  handler: async (ctx, args) => {
    return await ctx.db
      .query("messages")
      .withIndex("by_channel", (q) => q.eq("channelId", args.channelId))
      .order("desc")
      .paginate(args.paginationOpts);
  },
});
```

```typescript
// React component with pagination
function MessageList({ channelId }: { channelId: Id<"channels"> }) {
  const { results, status, loadMore } = usePaginatedQuery(
    api.messages.list,
    { channelId },
    { initialNumItems: 25 }
  );

  return (
    <div>
      {results.map((message) => (
        <Message key={message._id} message={message} />
      ))}

      {status === "CanLoadMore" && (
        <button onClick={() => loadMore(25)}>Load More</button>
      )}

      {status === "LoadingMore" && <Loading />}
    </div>
  );
}
```

## Presence Indicators

### Schema

```typescript
// convex/schema.ts
export default defineSchema({
  presence: defineTable({
    odcumentId: v.string(),
    odcumentType: v.string(),
    lastSeen: v.number(),
  })
    .index("by_user", ["userId"])
    .index("by_document", ["documentId", "documentType"]),
});
```

### Update Presence

```typescript
// convex/presence.ts
export const heartbeat = mutation({
  args: {
    documentId: v.string(),
    documentType: v.string(),
  },
  returns: v.null(),
  handler: async (ctx, args) => {
    const identity = await ctx.auth.getUserIdentity();
    if (!identity) return null;

    const existing = await ctx.db
      .query("presence")
      .withIndex("by_user", (q) => q.eq("userId", identity.subject))
      .filter((q) =>
        q.and(
          q.eq(q.field("documentId"), args.documentId),
          q.eq(q.field("documentType"), args.documentType)
        )
      )
      .unique();

    if (existing) {
      await ctx.db.patch(existing._id, { lastSeen: Date.now() });
    } else {
      await ctx.db.insert("presence", {
        userId: identity.subject,
        documentId: args.documentId,
        documentType: args.documentType,
        lastSeen: Date.now(),
      });
    }
    return null;
  },
});

export const getActive = query({
  args: {
    documentId: v.string(),
    documentType: v.string(),
  },
  returns: v.array(v.object({
    userId: v.string(),
    lastSeen: v.number(),
  })),
  handler: async (ctx, args) => {
    const fiveMinutesAgo = Date.now() - 5 * 60 * 1000;

    return await ctx.db
      .query("presence")
      .withIndex("by_document", (q) =>
        q.eq("documentId", args.documentId).eq("documentType", args.documentType)
      )
      .filter((q) => q.gt(q.field("lastSeen"), fiveMinutesAgo))
      .collect();
  },
});
```

### Client Hook

```typescript
function usePresence(documentId: string, documentType: string) {
  const heartbeat = useMutation(api.presence.heartbeat);
  const activeUsers = useQuery(api.presence.getActive, {
    documentId,
    documentType,
  });

  useEffect(() => {
    // Send heartbeat every 30 seconds
    const interval = setInterval(() => {
      heartbeat({ documentId, documentType });
    }, 30000);

    // Initial heartbeat
    heartbeat({ documentId, documentType });

    return () => clearInterval(interval);
  }, [documentId, documentType, heartbeat]);

  return activeUsers ?? [];
}
```

## Typing Indicators

```typescript
// convex/typing.ts
export const setTyping = mutation({
  args: { channelId: v.id("channels"), isTyping: v.boolean() },
  returns: v.null(),
  handler: async (ctx, args) => {
    const identity = await ctx.auth.getUserIdentity();
    if (!identity) return null;

    const existing = await ctx.db
      .query("typing")
      .withIndex("by_channel_user", (q) =>
        q.eq("channelId", args.channelId).eq("userId", identity.subject)
      )
      .unique();

    if (args.isTyping) {
      if (existing) {
        await ctx.db.patch(existing._id, { updatedAt: Date.now() });
      } else {
        await ctx.db.insert("typing", {
          channelId: args.channelId,
          userId: identity.subject,
          updatedAt: Date.now(),
        });
      }
    } else if (existing) {
      await ctx.db.delete(existing._id);
    }
    return null;
  },
});

export const getTyping = query({
  args: { channelId: v.id("channels") },
  returns: v.array(v.string()),
  handler: async (ctx, args) => {
    const identity = await ctx.auth.getUserIdentity();
    const tenSecondsAgo = Date.now() - 10000;

    const typing = await ctx.db
      .query("typing")
      .withIndex("by_channel", (q) => q.eq("channelId", args.channelId))
      .filter((q) => q.gt(q.field("updatedAt"), tenSecondsAgo))
      .collect();

    // Exclude current user
    return typing
      .filter((t) => t.userId !== identity?.subject)
      .map((t) => t.userId);
  },
});
```

## Conditional Queries

```typescript
function UserProfile({ userId }: { userId: Id<"users"> | null }) {
  // Query only runs when userId is not null
  const user = useQuery(
    api.users.get,
    userId ? { userId } : "skip"
  );

  if (userId === null) return <GuestView />;
  if (user === undefined) return <Loading />;

  return <ProfileView user={user} />;
}
```

## Common Pitfalls

- **Stale optimistic updates** - Always verify server state matches expected
- **Over-subscribing** - Only subscribe to data you need
- **Missing loading states** - Handle `undefined` (loading) vs `null` (not found)
- **Presence cleanup** - Add scheduled job to clean old presence records

## References

- Reactivity: https://docs.convex.dev/client/react
- Optimistic Updates: https://docs.convex.dev/client/react/optimistic-updates
- Pagination: https://docs.convex.dev/database/pagination


---
Source attribution: aaronvanston
Original project: https://github.com/aaronvanston/skills-convex/blob/5ea8c54ce73b814da9d50d384765c1501c76d999/skills/convex-realtime/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: aaronvanston
Original project: https://github.com/aaronvanston/skills-convex/blob/5ea8c54ce73b814da9d50d384765c1501c76d999/skills/convex-realtime/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Frontend Developer, Growth Product Manager, Product Manager
Specialties: API, Frontend
Tools: Convex
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 096b12ffcde7e4f47a8be20bff19241067e41b6f5de32d5e42c9b8d2240a40ac