Hydration Strategies

strategy= on <cf_Island> controls when (and whether) the component is rendered.

Strategy	SSR’d HTML?	Client boots when…
load	yes	the module loads (default)
idle	yes	requestIdleCallback fires
visible	yes	the mount enters the viewport (IntersectionObserver)
client	no	the module loads (no SSR HTML or CSS is emitted)

When to use each

• load — small, above-the-fold widgets that need to be interactive immediately.
• idle — non-critical interactivity (analytics opt-ins, comment widgets) that should wait for the main thread to free up.
• visible — long pages where most islands are below the fold. Avoids paying hydration cost for things the user may never scroll to.
• client — components that depend on browser-only APIs (window, IndexedDB, MediaDevices, etc.) or where SSR isn’t worth the round-trip.

How it works

Each strategy compiles to a different boot wrapper around the framework’s mount() call:

• load / client: bare <script type="module"> that mounts immediately.
• idle: wrapped in requestIdleCallback (with a setTimeout(200) fallback).
• visible: wrapped in an IntersectionObserver on the mount element. Observer disconnects after the first intersection.

For client, Coldspa skips the SSR sidecar call entirely — no HTML, no CSS pre-render — and the framework client uses createApp (Vue) or createRoot (React) instead of the hydration variant.