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Presence, Cursors, and Activity

Sometimes you want to show real-time updates to users without persisting the data to your database. Common scenarios include:

  • Shared cursors in a collaborative whiteboard like Figma
  • Who's online in a document editor like Google Docs
  • Typing indicators in chat apps like Discord
  • Live reactions in a video streaming app like Twitch

Instant provides three primitives for quickly building these ephemeral experiences: rooms, presence, and topics.

Rooms

A room represents a temporary context for realtime events. Users in the same room will receive updates from every other user in that room.

Presence

Presence is an object that each peer shares with every other peer. When a user updates their presence, it's instantly replicated to all users in that room. Presence persists throughout the remainder of a user's connection, and is automatically cleaned up when a user leaves the room

You can use presence to build features like "who's online." Instant's cursor and typing indicator are both built on top of the presence API.

Topics

Topics have "fire and forget" semantics, and are better suited for data that don't need any sort of persistence. When a user publishes a topic, a callback is fired for every other user in the room listening for that topic.

You can use topics to build features like "live reactions." The real-time emoji button panel on Instant's homepage is built using the topics API.

Transact vs. Epehemeral

You may be thinking when would I use transact vs presence vs topics? Here's a simple breakdown:

  • Use transact when you need to persist data to the db. For example, when a user sends a message in a chat app.
  • Use presence when you need to persist data in a room but not to the db. For example, showing who's currently viewing a document.
  • Use topics when you need to broadcast data to a room, but don't need to persist it. For example, sending a live reaction to a video stream.

Setup

To obtain a room reference, call db.room(roomType, roomId)

// db will export all the presence hooks you need!
const db = init<Schema>({ appId: APP_ID })

const room = db.room('video', '123')

Typing

You can provide typings for presence and topics as generic parameters.

// Generic type for room schemas.
type RoomSchemaShape = {
  [roomType: string]: {
    presence?: { [k: string]: any };
    topics?: {
      [topic: string]: {
        [k: string]: any;
      };
    };
  };
};

// A concrete example
type RoomSchema {
  video: {
    presence: { handle: string; avatarUrl: string; color: string };
    topics: {
      reaction: { emoji: string };
    };
  };
}

// db with typings for presence and topics!
const db = init<Schema, RoomSchema>({ appId })

// room handle
const room = db.room('video', '123')

Presence

Instant's usePresence is similar in feel to useState. it returns an object containing the current user's presence state, the presence state of every other user in the room, and a function (publishPresence) to update the current user's presence. publishPresence is similar to React's setState, and will merge the current and new presence objects.

const room = db.room('chat', 'chatRoomId')

const { user, peers, publishPresence } = room.usePresence()

useEffect(() => {
  publishPresence({ name: 'joe' })
}, [])

usePresence accepts a second parameter to select specific slices of user's presence object.

const room = db.room('chat', 'chatRoomId')
// will only return the `status` value for each peer
// will only trigger an update when a user's `status` value changes (ignoring any other changes to presence).
// This is useful for optimizing re-renders in React.

const { user, peers, publishPresence } = room.usePresence({
  keys: ['status'],
})

You may also specify an array of peers and a user flag to further constrain the output. If you wanted a "write-only" hook, it would look like this:

// Will not trigger re-renders on presence changes
const room = db.room('chat', 'chatRoomId')

const { publishPresence } = room.usePresence({
  peers: [],
  user: false,
})

Topics

Instant provides 2 hooks for sending and handling events for a given topic. usePublishTopic returns a function you can call to publish an event, and useTopicEffect will be called each time a peer in the same room publishes a topic event.

const room = db.room('video', 'videoId')
const publishEmote = room.usePublishTopic('emotes')

room.useTopicEffect('emotes', (event, peer) => {
  // Render broadcasted emotes!
  renderEmote(event.emoji)
})

return <button onClick={() => publishEmote({ emoji: '🔥' })}>🔥</button>

Cursors and Typing Indicators (React only)

We wanted to make adding real-time features to your apps as simple as possible, so we shipped our React library with 2 drop-in utilities: Cursors and useTypingIndicator.

Cursors

Adding multiplayer cursors to your app is as simple as importing our <Cursors> component!

import { Cursors } from '@instantdb/react'

// ...

return (
  <Cursors room={room} currentUserColor="tomato">
    {/* Your app here */}
  </Cursors>
)

You can provide a renderCursor function to return your own custom cursor component.

<Cursors
  room={room}
  className="cursors"
  currentUserColor="papayawhip"
  renderCursor={renderCoolCustomCursor}
/>

You can render multiple cursor spaces. For instance, imagine you're building a screen with multiple tabs. You want to only show cursors on the same tab as the current user. You can provide each <Cursors /> element with their own spaceId.

<Tabs>
  {tabs.map((tab) => (
    <Tab>
      <Cursors room={room} spaceId={`tab-${tab.id}`} className="tab-cursor">
        {/* ... */}
      </Cursors>
    </Tab>
  ))}
</Tabs>

You can even nest <Cursors />!

<Cursors
  room={room}
  spaceId="space-outer"
  userCursorColor="magenta"
  className="cursors-nested-outer"
>
  <Cursors
    room={room}
    spaceId="space-inner"
    userCursorColor="blue"
    className="cursors-nested-inner"
  />
</Cursors>

Typing indicators

useTypingIndicator is a small utility useful for building inputs for chat-style apps. You can use this hook to show things like "Peer is typing..." in your chat app.

import { init } from '@instantdb/react';

const db = init({ appId: "REPLACE ME" });

const randomId = Math.random().toString(36).slice(2, 6);
const user = {
  name: `${randomId}`,
};

const room = db.room('typing-indicator-example', '1234');

export default function InstantTypingIndicator() {
  // 1. Set your presence in the room
  room.useSyncPresence(user);

  // 2. Use the typing indicator hook
  const typing = room.useTypingIndicator('chat');

  const onKeyDown = (e) => {
    // 3. Render typing indicator
    typing.inputProps.onKeyDown(e);

    // 4. Optionally run your own onKeyDown logic
    if (e.key === 'Enter' && !e.shiftKey) {
      e.preventDefault();
      console.log('Message sent:', e.target.value);
    }
  };

  return (
    <div className="flex h-screen gap-3 p-2">
      <div key="main" className="flex flex-1 flex-col justify-end">
        <textarea
          onKeyBlur={typing.inputProps.onBlur}
          onKeyDown={onKeyDown}
          placeholder="Compose your message here..."
          className="w-full rounded-md border-gray-300 p-2 text-sm"
        />
        <div className="truncate text-xs text-gray-500">
          {typing.active.length ? typingInfo(typing.active) : <>&nbsp;</>}
        </div>
      </div>
    </div>
  );
}

function typingInfo(users) {
  if (users.length === 0) return null;
  if (users.length === 1) return `${users[0].name} is typing...`;
  if (users.length === 2)
    return `${users[0].name} and ${users[1].name} are typing...`;

  return `${users[0].name} and ${users.length - 1} others are typing...`;
}