<Async>

The <Async> component is meant for asynchronous rendering. E.g. loading page content.

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import { Async } from "rvx/async";

// main.tsx:
<Async source={() => import("./page")}>
    {page => <page.content />}
</Async>

// page.tsx:
export function content() {
    return <h1>Hello World!</h1>;
}

import { Async } from "./rvx.js";

// main.js:
Async({
    source: () => import("./page"),
    children: page => page.content(),
})

// page.js:
export function content() {
    return e("h1").append("Hello World!");
}

The rejected and pending properties can be used for rendering content when the promise is rejected or pending:

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<Async
    source={() => import("./page")}
    pending={() => <>Loading...</>}
    rejected={error => <>Error: {error}</>}
>
    {page => <page.content />}
</Async>

Async({
    source: () => import("./page"),
    pending: () => "Loading...",
    rejected: error => ["Error: ", error],
    children: page => page.content(),
})

Tracking Completion

To wait for async parts in a specific context to complete, you can use AsyncContexts:

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import { Inject } from "rvx";
import { ASYNC, Async, AsyncContext } from "rvx/async";

const ctx = new AsyncContext();

<Inject key={ASYNC} value={ctx}>
    {() => <Async>...</Async>}
</Inject>

// Wait for all "<Async>" parts to complete and re-throw unhandled errors:
await ctx.complete();

// Or manually track an async task:
ctx.track(fetch("something"));

import { inject, ASYNC, Async, AsyncContext } from "./rvx.js";

const ctx = new AsyncContext();

inject(ASYNC, ctx, () => {
    return Async({ ... });
})

// Wait for all "<Async>" parts to complete and re-throw unhandled errors:
await ctx.complete();

// Or manually track an async task:
ctx.track(fetch("something"));

Revealing Content At Once

When there are multiple async parts in the same place, tracking can be used to hide an entire area and show it once all of the inner async parts have completed.

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import { Inject, sig, movable } from "rvx";
import { ASYNC, Async, AsyncContext } from "rvx/async";

const innerCtx = new AsyncContext();
const inner = movable(
    <Inject key={ASYNC} value={innerCtx}>
        {() => <>
            <Async>...</Async>
            <Async>...</Async>
            <Async>...</Async>
        </>}
    </Inject>
);

<Async source={innerCtx.complete()}>
    {() => inner.move()}
</Async>

import { inject, sig, movable, ASYNC, Async, AsyncContext } from "./rvx.js";

const innerCtx = new AsyncContext();
const inner = movable(inject(ASYNC, innerCtx, () => [
    Async({ ... }),
    Async({ ... }),
    Async({ ... }),
]));

Async({
    source: innerCtx.complete(),
    children: () => inner.move(),
})

Dynamic Sources

The <Show> or <Nest> components can be used to replace the source property over time:

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<Show when={someSignal}>
    {source => <Async source={source}>...</Async>}
</Show>

Show({
    when: someSignal,
    children: source => Async({ source, ... })
})

The example below fetches a file and aborts pending requests when the file name is changed early:

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const name = sig("example.txt");

<Nest>
    {() => {
        const value = name.value;
        return () => <Async source={fetch(value, { signal: useAbortSignal() }).then(r => r.text())}>
            {text => <pre>{text}</pre>}
        </Async>;
    }}
</Nest>

const name = sig("example.txt");

Nest({
    children: () => {
        const value = name.value;
        return () => Async({
            source: fetch(value, { signal: useAbortSignal() }).then(r => r.text()),
            children: text => e("pre").append(text),
        });
    },
})