astro/dist/prefetch/vite-plugin-prefetch.js

Astro is a modern site builder with web best practices, performance, and DX front-of-mind.

const VIRTUAL_MODULE_ID = "astro:prefetch";
const RESOLVED_VIRTUAL_MODULE_ID = "\0" + VIRTUAL_MODULE_ID;
const prefetchInternalModuleFsSubpath = "astro/dist/prefetch/index.js";
const prefetchCode = `import { init } from 'astro/virtual-modules/prefetch.js';init()`;
export default function astroPrefetch({ settings }) {
	const prefetchOption = settings.config.prefetch;
	const prefetch = prefetchOption ? typeof prefetchOption === "object" ? prefetchOption : {} : undefined;
	// Check against existing scripts as this plugin could be called multiple times
	if (prefetch && settings.scripts.every((s) => s.content !== prefetchCode)) {
		// Inject prefetch script to all pages
		settings.scripts.push({
			stage: "page",
			content: `import { init } from 'astro/virtual-modules/prefetch.js';init()`
		});
	}
	// Throw a normal error instead of an AstroError as Vite captures this in the plugin lifecycle
	// and would generate a different stack trace itself through Vite's transform pipeline.
	const throwPrefetchNotEnabledError = () => {
		throw new Error("You need to enable the `prefetch` Astro config to import `astro:prefetch`");
	};
	return {
		name: "astro:prefetch",
		resolveId: {
			filter: { id: new RegExp(`^${VIRTUAL_MODULE_ID}$`) },
			handler() {
				if (!prefetch) throwPrefetchNotEnabledError();
				return RESOLVED_VIRTUAL_MODULE_ID;
			}
		},
		load: {
			filter: { id: new RegExp(`^${RESOLVED_VIRTUAL_MODULE_ID}$`) },
			handler() {
				if (!prefetch) throwPrefetchNotEnabledError();
				return { code: `export { prefetch } from "astro/virtual-modules/prefetch.js";` };
			}
		},
		transform: {
			filter: { 
			// NOTE: Handle replacing the specifiers even if prefetch is disabled so View Transitions
			// can import the internal module and not hit runtime issues.
id: new RegExp(`${prefetchInternalModuleFsSubpath}`) },
			handler(code) {
				// We perform a simple replacement with padding so that the code offset is not changed and
				// we don't have to generate a sourcemap. This has the assumption that the replaced string
				// will always be shorter than the search string to work.
				code = code.replace("__PREFETCH_PREFETCH_ALL__", `${JSON.stringify(prefetch?.prefetchAll)}`.padEnd(25)).replace("__PREFETCH_DEFAULT_STRATEGY__", `${JSON.stringify(prefetch?.defaultStrategy)}`.padEnd(29)).replace("__EXPERIMENTAL_CLIENT_PRERENDER__", `${JSON.stringify(settings.config.experimental.clientPrerender)}`.padEnd(33));
				return {
					code,
					map: null
				};
			}
		}
	};
}