Send HTML shell early, stream completed segments as async data resolves — improves TTFB vs buffer-all SSR.

Web Platform APIs

Streaming SSR

<h2>Summary</h2>
<p>Only interactive subtrees hydrate; static HTML stays inert — reduces JS execution at load. Differs from full hydration and progressive enhancement. Framework must not ship client bundle for static regions. Pair with <a href="#27-selective-hydration">2.7 Selective hydration</a>.</p>
<h2>Code example</h2>
<pre><code class="language-javascript">// Static shell — no hydration
const staticHtml = renderToString(&lt;Article body={markdown} /&gt;);

// Interactive island only
hydrateRoot(document.querySelector('#comments'), &lt;CommentForm /&gt;);
</code></pre>
<h2>Key points</h2>
<ul>
<li>Only interactive subtrees hydrate; static HTML stays inert — reduces JS execution at load.</li>
<li>Differs from full hydration and progressive enhancement.</li>
<li>Framework must not ship client bundle for static regions.</li>
<li>Pair with <a href="#27-selective-hydration">2.7 Selective hydration</a>.</li>
</ul>
<h2>Further reading</h2>
<ul>
<li><a href="https://web.dev/articles/performance-patterns-for-web-apps">Partial hydration patterns</a></li>
<li><a href="https://react.dev/reference/rsc/use-client">Client Components</a></li>
</ul>
<h2>Related concepts</h2>
<ul>
<li><a href="/blogs/level-7-islands-architecture">Islands architecture</a></li>
<li><a href="/blogs/level-7-streaming-ssr">Streaming SSR</a></li>
</ul>


Only interactive subtrees hydrate; static HTML stays inert — reduces JS execution at load.

Partial hydration

Static HTML shell with small hydrated interactive islands — minimal JS vs full SPA.