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Preloader in Rollup
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| package-lock.json | |
| build | |
| node_modules |
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| export function exclaim(msg) { | |
| return msg + "!"; | |
| } |
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| <!DOCTYPE html> | |
| <script type="module" src="index.js"></script> |
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| setTimeout(async () => { | |
| const { shout } = | |
| Math.random() < 0.5 | |
| ? await import("./utilsA.js") | |
| : await import("./utilsB.js"); | |
| shout("this is index"); | |
| }, 1000); |
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| { | |
| "name": "rollup-parallel", | |
| "scripts": { | |
| "build": "rollup -c && cp index.html build/" | |
| } | |
| } |
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| const MARKER = "preloading-import:"; | |
| const PLACEHOLDER = "____TOTALLY_A_PLACEHOLDER____"; | |
| export default function preload() { | |
| return { | |
| name: "preload", | |
| resolveId(id) { | |
| if (id !== MARKER) { | |
| return; | |
| } | |
| return id; | |
| }, | |
| load(id) { | |
| if (id !== MARKER) { | |
| return; | |
| } | |
| return ` | |
| const bundleData = ${PLACEHOLDER}; | |
| export async function preloadingImport(path, base) { | |
| const deps = new Set([path]); | |
| for(const dep of deps) { | |
| for(const subdep of (bundleData[dep] || [])) { | |
| deps.add(subdep); | |
| } | |
| } | |
| for(const dep of deps) { | |
| const tag = document.createElement("link"); | |
| tag.rel = "preload"; | |
| tag.as = "script" | |
| tag.crossOrigin = true; | |
| tag.href = dep; | |
| document.head.append(tag); | |
| }; | |
| return import(path); | |
| } | |
| `; | |
| }, | |
| transform(code, id) { | |
| if (!code.includes("import(")) { | |
| return; | |
| } | |
| if (id === MARKER) { | |
| return; | |
| } | |
| return ` | |
| import {preloadingImport} from "${MARKER}"; | |
| // Rollup prunes the import because renderDynamicImport() | |
| // didn’t run yet. This is my workaround. | |
| self[Symbol()] = preloadingImport; | |
| ${code} | |
| `; | |
| }, | |
| renderDynamicImport({ moduleId }) { | |
| if (moduleId === MARKER) { | |
| return; | |
| } | |
| return { | |
| left: "preloadingImport(", | |
| right: ", import.meta.url)" | |
| }; | |
| }, | |
| generateBundle(options, bundle) { | |
| const bundleData = {}; | |
| for (const [fileName, info] of Object.entries(bundle)) { | |
| if (info.type !== "chunk") { | |
| continue; | |
| } | |
| bundleData[fileName] = info.imports; | |
| } | |
| for (const chunk of Object.values(bundle)) { | |
| chunk.code = chunk.code.replace( | |
| PLACEHOLDER, | |
| JSON.stringify(bundleData) | |
| ); | |
| } | |
| } | |
| }; | |
| } |
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| import preload from "./rollup-plugin-preload.js"; | |
| export default { | |
| input: "index.js", | |
| output: { | |
| dir: "build", | |
| format: "esm" | |
| }, | |
| plugins: [preload()] | |
| }; |
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| import { exclaim } from "./exclaim.js"; | |
| export function logCaps(msg) { | |
| if (!msg) return; | |
| console.log(msg.toUpperCase()); | |
| } | |
| export function shout(msg) { | |
| logCaps(exclaim(msg)); | |
| } |
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| import { exclaim } from "./exclaim.js"; | |
| export function logNormal(msg) { | |
| if (!msg) return; | |
| console.log(msg); | |
| } | |
| export function shout(msg) { | |
| logNormal(exclaim(msg)); | |
| } |
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