`Suspense` and `async` Component Support

[shellscape]

Hey thanks for the package! Any chance of getting Suspense and async support? For reference, hono just added experimental support for that concept https://github.com/honojs/hono/blob/next/src/jsx/streaming.ts#L25

[i-like-robots]

Thanks for your question @shellscape.

I have considered implementing a streaming - async - renderer before because JSX is so slow compared to string based template libraries like Handlebars. However, I've not had a reason to invest effort into this.

Because this library doesn't handle state I think any <Suspense> implementation would be very basic - either always rendering the fallback or always waiting for its children to resolve. It's certainly possible to support this to avoid erroring if nothing else.

[shellscape]

@i-like-robots we're currently using a mishmashed jsx renderer, with a significant portion based on hyperons. we've integrated Suspense support here: https://github.com/shellscape/jsx-email/blob/afd9ca80fe1111e17796901f7bd6c0187c0a0de5/packages/jsx-email/src/render/jsx-to-string.ts#L93-L143

It works well with all of our testing and userland use. Hopefully that's helpful for hyperons.

[i-like-robots]

Thank you @shellscape that's very interesting. And I'm really pleased to hear the code has been useful for more people 👍

[i-like-robots]

I've added a very basic shim for the <Suspense> component in #51

Longer term, I think supporting async components could be really interesting - not many templating languages do this well but it feels like it could be a fairly natural fit for JSX.