---
title: Live updates
description: Show changes to everyone looking at an app as they happen, with watch on collections and crow.live channels for messages that aren't saved.
---

# Live updates

There are two kinds of live updates:

- **Saved data that updates for everyone.** Use `watch` on a collection: when anyone adds or changes a document, every open page gets the new list. See [Data](/data#watch-for-changes).
- **Messages that aren't saved.** Cursors, typing indicators, game moves. Use a `crow.live` channel.

## Turn on channels

```json
{ "live": { "who": "viewers" } }
```

`who` is `viewers` (signed-in people who can open the app, the default) or `public` (signed-out visitors too, public apps only). Without a `live` section, `watch` still updates live for anyone who can read the collection; only channels need it.

## Use a channel

```js
const room = crow.live.channel("board");

room.on("message", (data, from) => move(data));   // from = { userId, visitor }
room.on("presence", (people) => showWho(people));  // who is in the channel now
room.send({ x: 10, y: 20 });                       // any JSON, up to 4 KB
room.leave();
```

Everyone in the same app who joins a channel with the same name gets each message. Messages aren't stored: someone who joins later doesn't see earlier ones. Save anything that should last with [crow.db](/data).