Emit runtime asset manifest as ESM module

src/server/PublicAssetManifest.ts

@@ -141,11 +141,15 @@ export function copyRootPublicFiles(
   }
 }
 
-export function writePublicAssetManifestFile(
+export function writePublicAssetManifestModule(
   outDir: string,
   assetManifest: AssetManifest,
 ): void {
-  const manifestPath = path.join(outDir, "_assets", "asset-manifest.json");
+  const manifestPath = path.join(outDir, "_assets", "asset-manifest.mjs");
   fs.mkdirSync(path.dirname(manifestPath), { recursive: true });
-  fs.writeFileSync(manifestPath, `${JSON.stringify(assetManifest, null, 2)}\n`);
+  const serializedManifest = JSON.stringify(assetManifest, null, 2);
+  fs.writeFileSync(
+    manifestPath,
+    `const assetManifest = ${serializedManifest};\nexport { assetManifest };\nexport default assetManifest;\n`,
+  );
 }

src/server/RuntimeAssetManifest.ts

@@ -1,18 +1,25 @@
-import fs from "fs/promises";
 import path from "path";
-import { fileURLToPath } from "url";
+import { fileURLToPath, pathToFileURL } from "url";
 import type { AssetManifest } from "../core/AssetUrls";
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
 const staticDir = path.join(__dirname, "../../static");
-const manifestPath = path.join(staticDir, "_assets", "asset-manifest.json");
+const manifestPath = path.join(staticDir, "_assets", "asset-manifest.mjs");
 
 let manifestPromise: Promise<AssetManifest> | null = null;
+let manifestVersion = 0;
 
-async function readRuntimeAssetManifest(): Promise<AssetManifest> {
-  const raw = await fs.readFile(manifestPath, "utf8");
-  return JSON.parse(raw) as AssetManifest;
+async function importRuntimeAssetManifest(
+  version: number,
+): Promise<AssetManifest> {
+  const manifestModule = (await import(
+    `${pathToFileURL(manifestPath).href}?v=${version}`
+  )) as {
+    assetManifest?: AssetManifest;
+    default?: AssetManifest;
+  };
+  return manifestModule.assetManifest ?? manifestModule.default ?? {};
 }
 
 export async function getRuntimeAssetManifest(): Promise<AssetManifest> {
@@ -20,10 +27,11 @@ export async function getRuntimeAssetManifest(): Promise<AssetManifest> {
     return {};
   }
 
-  manifestPromise ??= readRuntimeAssetManifest();
+  manifestPromise ??= importRuntimeAssetManifest(manifestVersion);
   return manifestPromise;
 }
 
 export function clearRuntimeAssetManifestCache(): void {
+  manifestVersion++;
   manifestPromise = null;
 }

vite.config.ts

@@ -11,7 +11,7 @@ import {
   copyRootPublicFiles,
   createHashedPublicAssetFiles,
   getResourcesDir,
-  writePublicAssetManifestFile,
+  writePublicAssetManifestModule,
 } from "./src/server/PublicAssetManifest";
 
 // Vite already handles these, but its good practice to define them explicitly
@@ -44,7 +44,7 @@ export default defineConfig(({ mode }) => {
     closeBundle() {
       const outDir = path.join(__dirname, "static");
       copyRootPublicFiles(resourcesDir, outDir);
-      writePublicAssetManifestFile(outDir, assetManifest);
+      writePublicAssetManifestModule(outDir, assetManifest);
       createHashedPublicAssetFiles(resourcesDir, outDir, assetManifest);
     },
   });