Lazy hubs

By default, the library connects every hub in the contract when the app starts. A lazy hub connects only when a consumer needs it. Set lazy: true for one hub, or for all hubs.

Grace periodCopy Anchor Link

graceMs is the time that a lazy hub stays connected after its last consumer leaves. A short grace period prevents a disconnect and a new connect when a component remounts quickly. The default is 0. graceMs is a per-hub option.

When the grace period ends, the hub stops and its status is "idle". When a consumer comes back, the hub connects again.

What counts as a consumerCopy Anchor Link

The library counts the consumers of each hub. The hub is wanted while the count is more than 0. A consumer is not a component. It is one call of a helper that is bound to a hub.

Each of these counts as a consumer for the hub that you pass:

• keepHubAlive, which keeps the hub connected and does nothing else.
• onHubEvent, hubInvoke, hubSend, and hubTeardown.
• hubStatus and onReconnected.

The consumer ends when the component is destroyed.

A status banner for a lazy hub also connects that hub. To read the status without a connection, use getSignalR. Its getStatus function does not count as a consumer.

Here, a component keeps the lazy presence hub alive and shows its online count:

<script lang="ts">
  import { onHubEvent } from "./client";

  let count = $state(0);

  // The subscription keeps the lazy hub connected while this component lives.
  onHubEvent("/hubs/presence", "OnlineCount", (online) => {
    count = online;
  });
</script>

<p>{count} online</p>

A teardown call holds a lazy hub open until it is sent, even after its own consumer leaves.