在线状态与广播频道
借助 Supabase Realtime Presence 跟踪在线用户，并使用 Broadcast 在客户端之间发送临时消息，不再局限于监听表变更。
在线状态与广播频道 是 CoddyKit 上的免费 Supabase Backend as a Service 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Supabase Backend as a Service 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Supabase Backend as a Service 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Two More Realtime Features
Besides Postgres change streams, Supabase Realtime offers Presence (track online users) and Broadcast (send transient messages). Neither requires a database table.
What Is Presence?
Presence lets each client share small state (like a username or cursor position) and see everyone else's state in the same channel in real time.
Creating a Channel
A channel is a named room clients join.
const room = supabase.channel('room-1', {
config: { presence: { key: 'user-42' } }
});Tracking Presence
After subscribing, call track to publish your state to everyone in the channel.
room.subscribe(async (status) => {
if (status === 'SUBSCRIBED') {
await room.track({ name: 'Ada', online_at: Date.now() });
}
});Reading Who Is Online
Listen for sync events and read the current presence state of all members.
room.on('presence', { event: 'sync' }, () => {
const state = room.presenceState();
console.log('Online:', Object.keys(state).length);
});Join and Leave Events
Presence emits join and leave events so you can animate users appearing and disappearing.
room.on('presence', { event: 'join' }, ({ newPresences }) => {
console.log('Joined:', newPresences.length);
});What Is Broadcast?
Broadcast sends low-latency messages to everyone in a channel without storing them. Great for cursors, typing indicators, and game moves.
Sending a Broadcast
Use send with a custom event name and payload.
room.send({
type: 'broadcast',
event: 'cursor',
payload: { x: 120, y: 80 }
});Receiving a Broadcast
Subscribe to the same event name to handle incoming messages.
room.on('broadcast', { event: 'cursor' }, ({ payload }) => {
console.log('Cursor at', payload.x, payload.y);
});Cleaning Up
Always remove channels when a component unmounts to free connections.
function cleanup(channel, supabase) {
supabase.removeChannel(channel);
return 'removed';
}
console.log(cleanup('chan', { removeChannel: () => {} }));Choosing the Right Tool
Use Postgres changes for persisted data, Presence for online status, and Broadcast for fast disposable messages.
Quick Check
Test your understanding of Presence and Broadcast.
Recap
You learned to track online users with Presence and send ephemeral messages with Broadcast, plus when to use each versus Postgres change streams, and to clean up channels.
用 AI 导师学习 Supabase Backend as a Service — 免费
在浏览器中编写并运行真实代码，获得全天候 AI 导师的即时帮助，并在网页或应用中继续学习。
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常见问题解答
「在线状态与广播频道」课时是免费的吗？
是的 — 「在线状态与广播频道」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Supabase Backend as a Service 课程的其余内容，请升级到 CoddyKit PRO。 Supabase Backend as a Service 课程共包含 4 节课。
「在线状态与广播频道」这节课中我会学到什么？
借助 Supabase Realtime Presence 跟踪在线用户，并使用 Broadcast 在客户端之间发送临时消息，不再局限于监听表变更。 你通过在浏览器中直接运行的动手代码来练习 Supabase Backend as a Service，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Supabase Backend as a Service 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Supabase Backend as a Service 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「在线状态与广播频道」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Supabase Backend as a Service 课中编写并运行代码吗？
能。每节 Supabase Backend as a Service 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。