feat: use nitro to load polyfill at the earliest

src/module.ts

@@ -1,9 +1,9 @@
 import {
   defineNuxtModule,
-  addPlugin,
   addServerHandler,
   createResolver,
   extendViteConfig,
+  addServerPlugin,
 } from '@nuxt/kit'
 import { withQuery } from 'ufo'
 import polyfillist from 'polyfillist'
@@ -27,7 +27,8 @@ export default defineNuxtModule<ModuleOptions>({
     host: 'https://polyfill.io/v3/polyfill.min.js',
   },
   async setup (options, nuxt) {
-    const resolver   = createResolver(import.meta.url)
+    const resolver = createResolver(import.meta.url)
+
     const features   = await polyfillist(options.target)
     const isSelfHost = options.host === 'selfhost'
     const src        = options.host && !isSelfHost
@@ -37,8 +38,7 @@ export default defineNuxtModule<ModuleOptions>({
     nuxt.options.runtimeConfig.nupolyon        = { features }
     nuxt.options.runtimeConfig.public.nupolyon = { src, isSelfHost }
 
-    // Do not add the extension since the `.ts` will be transpiled to `.mjs` after `npm run prepack`
-    addPlugin(resolver.resolve('./runtime/plugin'))
+    addServerPlugin(resolver.resolve('./runtime/server/plugins/polyfill'))
 
     if (isSelfHost) {
       addServerHandler({

src/runtime/server/plugins/polyfill.ts

@@ -0,0 +1,38 @@
+import { joinURL, cleanDoubleSlashes } from 'ufo'
+import { useRuntimeConfig } from "#imports";
+
+/**
+ * Due to an upstream bug in Nuxt 3 we need to stub the `defineNitroPlugin`.
+ * See https://github.com/nuxt/nuxt/issues/18556
+ *
+ * Once this issue is resolved, then this file can be updated to the following:
+ *
+ * ```ts
+ * import { defineNitroPlugin } from '#imports'
+ * ```
+ */
+import { NitroApp } from 'nitropack'
+
+export type NitroAppPlugin = (nitro: NitroApp) => void
+export function defineNitroPlugin (def: NitroAppPlugin): NitroAppPlugin {
+  return def
+}
+/**
+ * End of workaround
+ */
+
+export default defineNitroPlugin((nitroApp) => {
+  const config = useRuntimeConfig()
+
+  const { src, isSelfHost } = config.public.nupolyon
+  // Prepend the current runtime value of app.baseURL if configured for self-hosting
+  const host = !isSelfHost ? src : cleanDoubleSlashes(joinURL(config.app.baseURL, src))
+
+  if (host) {
+    // NOTE: By setting `nomodule` we make sure it executed directly upon loading, and also works in browsers which don't support ESM.
+    const polyfill = `<script src="${host}" crossorigin="anonymous" nomodule></script>`
+    nitroApp.hooks.hook('render:html', (html) => {
+      html.head.unshift(polyfill)  // insert at the beginning of the array
+    })
+  }
+})