Cursor

Same API as the core createCursor plugin, but cursor positions are shared across instances via Redis. Each instance throttles locally (same leading/trailing edge logic as the core), then relays broadcasts through Redis pub/sub so subscribers on other instances see cursor updates.

Hash entries have a TTL so stale cursors from crashed instances get cleaned up automatically.

When to use over the built-in plugin: The core cursor plugin broadcasts positions only to clients on the local process. In a multi-instance setup, users on different instances would not see each other’s cursors. The Redis version relays updates through pub/sub and stores positions in a shared hash.

Setup

// src/lib/server/cursors.js
import { redis } from './redis.js';
import { createCursor } from 'svelte-adapter-uws-extensions/redis/cursor';

export const cursors = createCursor(redis, {
  throttle: 50,
  select: (userData) => ({ id: userData.id, name: userData.name, color: userData.color }),
  ttl: 30
});

Usage

// src/hooks.ws.js
import { cursors } from '$lib/server/cursors';

export function message(ws, { data, platform }) {
  const msg = JSON.parse(Buffer.from(data).toString());
  if (msg.type === 'cursor') {
    cursors.update(ws, msg.topic, msg.position, platform);
  }
}

export function close(ws, { platform }) {
  cursors.remove(ws, platform);
}

Options

API