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Talking in real time

21 March 2026·2 min read

Cursors, game moves and chat need messages both ways as they happen. A channel opened by a component, and handled on the server in a few lines.

Live data covers pages that follow the database. Some things never touch the database: a cursor moving, a move in a game, a reading from a device. They need messages both ways, now, and gone a second later.

A channel

channel.on("game", (msg, peer) => {    // Everyone else in the channel sees the move.    channel.broadcast("game", { id: peer.id, pos: msg.pos }, { except: peer })})component Board() {    state others = {}    let game = channel.open("game", (m) => { others = set(others, m.id, m.pos) })    <canvas @pointermove={(e) => game.send({ pos: [e.clientX, e.clientY] })}/>}

In the browser, channel.open opens a channel for as long as the component is on the page, and .send sends a message to the server. On the server, channel.on handles each message, with peer saying who sent it, and answers one page, all of them, or none.

Who may join

Anyone who can open a page can ask to join a channel, so a channel for a private room needs a door. channel.on(name, f, { join }) decides: join(peer) sees the page's session, as it was when it connected, and says yes or no.

One connection

Channels share the page's single connection with live data and --watch reloads, so a page with a chat, a live list and a shared cursor still holds one socket. Messages to a handler arrive in order, one at a time, and a slow handler holds up no one else.

Read more: Real time in the docs.