Progressive HTML Rendering

ovr is a lightweight server framework built for streaming HTML with asynchronous generator JSX.

Introduction

Designed to optimize performance and Time-To-First-Byte (TTFB), ovr evaluates components in parallel and streams HTML in order by producing an AsyncGenerator of HTML that feeds directly into the streamed response.

For the following component:

tsx

function Component() {
	return <p>hello world</p>;
}

ovr generates three chunks of HTML:

"<p>"; // streamed immediately
"hello world"; // next
"</p>"; // last

While this is trivial for a paragraph, consider when a component is asynchronous:

tsx

async function Username() {
	const user = await getUser(); // slow...

	return <span>{user.name}</span>;
}

function Component() {
	return (
		<p>
			hello <Username />
		</p>
	);
}

Instead of waiting for Username to resolve before sending the entire Component, ovr will send what it has immediately and stream the rest as it becomes available.

"<p>";
"hello ";
// streamed immediately

// for await (const chunk of Username()) { ...
"<span>";
"username";
"</span>";
"</p>";

Web browsers are built for streaming, they parse and paint HTML as it arrives. Most critically, the <head> of the document can be sent immediately to start the requests for linked assets (JavaScript, CSS, etc.) before the page has finished rendering.

ovr’s architecture gives you true streaming SSR and progressive rendering out of the box. No hydration bundle, no buffering—just HTML delivered in order, as soon as it’s ready.

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