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| 1 | // TODO: revive the suspense renderer |
| 2 | /** |
| 3 | * This file implements out-of-order HTML streaming, mimicking the React |
| 4 | * Suspense API. To use, place Suspense around an expensive async component |
| 5 | * and render the page with 'renderStreaming'. |
| 6 | * |
| 7 | * Implementation of this article: |
| 8 | * https://lamplightdev.com/blog/2024/01/10/streaming-html-out-of-order-without-javascript/ |
| 9 | * |
| 10 | * I would link to an article from Next.js or React, but their examples |
| 11 | * are too verbose and not informative to what they actually do. |
| 12 | * @module |
| 13 | */ |
| 14 | const userData = render.userData<null | State>(() => null); |
| 15 | |
| 16 | export interface Input { |
| 17 | children: render.Node; |
| 18 | fallback?: render.Node; |
| 19 | } |
| 20 | |
| 21 | /** |
| 22 | * When used in combination with `Suspense.renderStreaming`, this component |
| 23 | * displays `fallback` until the async `children` `Node` has resolved.. |
| 24 | * |
| 25 | * return <div> |
| 26 | * <h1>page shell</h1> |
| 27 | * <Suspense fallback="Loading..."> |
| 28 | * <ComponentWithAwait /> |
| 29 | * </Suspense> |
| 30 | * </div>; |
| 31 | */ |
| 32 | export function Suspense({ children, fallback }: Input): render.Node { |
| 33 | const state = userData.get(); |
| 34 | if (!state) return children; |
| 35 | if (state.nested) throw new Error("<Suspense> cannot be nested"); |
| 36 | const parent = UNWRAP(render.current); |
| 37 | const r = render.init(true, { [userData.key]: { nested: true } }); |
| 38 | const resolved = render.resolveNode(r, children); |
| 39 | if (r.async == 0) return render.raw(resolved); |
| 40 | const name = "suspended_" + ++state.nextId; |
| 41 | state.nested = true; |
| 42 | const ip: [render.ResolvedNode] = [ |
| 43 | render.resolvedElement( |
| 44 | "slot", |
| 45 | { name }, |
| 46 | fallback ? render.resolveNode(parent, fallback) : "", |
| 47 | ), |
| 48 | ]; |
| 49 | state.nested = false; |
| 50 | r.asyncDone = () => { |
| 51 | const rejections = r.rejections; |
| 52 | if (rejections && rejections.length > 0) throw new Error("TODO"); |
| 53 | state.pushChunk?.(name, ip[0] = resolved); |
| 54 | }; |
| 55 | return render.raw(ip); |
| 56 | } |
| 57 | |
| 58 | // TODO: add a User-Agent parameter, which is used to determine if a |
| 59 | // fallback path must be used. |
| 60 | // - Before ~2024 needs to use a JS implementation. |
| 61 | // - IE should probably bail out entirely. |
| 62 | export async function* renderStreaming< |
| 63 | T extends render.Addons = Record<never, unknown>, |
| 64 | >(node: render.Node, addon: T = {} as T) { |
| 65 | const { |
| 66 | text: begin, |
| 67 | addon: { [userData.key]: state, ...addonOutput }, |
| 68 | } = await render.async(node, { |
| 69 | ...addon, |
| 70 | [userData.key]: { |
| 71 | nested: false, |
| 72 | nextId: 0, |
| 73 | completed: 0, |
| 74 | pushChunk: () => {}, |
| 75 | } satisfies State as State, |
| 76 | }); |
| 77 | if (state.nextId === 0) { |
| 78 | yield begin; |
| 79 | return addonOutput as unknown as T; |
| 80 | } |
| 81 | let resolve: (() => void) | null = null; |
| 82 | let chunks: string[] = []; |
| 83 | state.pushChunk = (slot, node) => { |
| 84 | while (node.length === 1 && Array.isArray(node)) node = UNWRAP(node[0]); |
| 85 | if (node[0] === render.kElement) { |
| 86 | (node as render.ResolvedElement)[2].slot = slot; |
| 87 | } else { |
| 88 | node = render.resolvedElement("clover-suspense", { |
| 89 | style: "display:contents", |
| 90 | slot, |
| 91 | }, node); |
| 92 | } |
| 93 | chunks.push(render.stringifyNode(node)); |
| 94 | resolve?.(); |
| 95 | }; |
| 96 | yield `<template shadowrootmode=open>${begin}</template>`; |
| 97 | do { |
| 98 | await new Promise<void>((done) => (resolve = done)); |
| 99 | yield* chunks; |
| 100 | chunks = []; |
| 101 | } while (state!.nextId < state!.completed); |
| 102 | return addonOutput as unknown as T; |
| 103 | } |
| 104 | |
| 105 | interface State { |
| 106 | nested: boolean; |
| 107 | nextId: number; |
| 108 | completed: number; |
| 109 | pushChunk(name: string, node: render.ResolvedNode): void; |
| 110 | } |
| 111 | |
| 112 | export declare namespace Suspense { |
| 113 | export type { Input }; |
| 114 | } |
| 115 | |
| 116 | import * as render from "lib/render.ts"; |