diff --git a/src/dev-bundler.ts b/src/dev-bundler.ts
new file mode 100644
index 0000000..4638808
--- /dev/null
+++ b/src/dev-bundler.ts
@@ -0,0 +1,189 @@
+import { builtinModules } from 'module'
+import * as vite from 'vite'
+import { uniq, hashId } from './utils'
+
+interface TransformChunk {
+  id: string
+  code: string
+  deps: string[]
+  parents: string[]
+}
+
+interface SSRTransformResult {
+  code: string
+  map: object
+  deps: string[]
+  dynamicDeps: string[]
+}
+
+async function transformRequest (viteServer: vite.ViteDevServer, id) {
+  // Virtual modules start with `\0`
+  if (id && id.startsWith('/@id/__x00__')) {
+    id = '\0' + id.slice('/@id/__x00__'.length)
+  }
+
+  if (id && id.startsWith('/@id/defaultexport')) {
+    id = id.slice('/@id/'.length)
+  }
+
+  // Externals
+  if (builtinModules.includes(id)) { // || id.includes('node_modules')) {
+    return {
+      code: `(global, exports, importMeta, ssrImport, ssrDynamicImport, ssrExportAll) => { ssrExportAll(require('${id.replace(/^\/@fs/, '')}')) }`,
+      deps: [],
+      dynamicDeps: []
+    }
+  }
+
+  // Transform
+  const res: SSRTransformResult = await viteServer.transformRequest(id, { ssr: true }).catch((err) => {
+    // eslint-disable-next-line no-console
+    console.warn(`[SSR] Error transforming ${id}: ${err}`)
+    // console.error(err)
+  }) as SSRTransformResult || { code: '', map: {}, deps: [], dynamicDeps: [] }
+
+  // Wrap into a vite module
+  const code = `async function (global, __vite_ssr_exports__, __vite_ssr_import_meta__, __vite_ssr_import__, __vite_ssr_dynamic_import__, __vite_ssr_exportAll__) {
+const module = __createCJSModule__(__vite_ssr_exports__)
+${res.code || '/* empty */'};
+}`
+  return { code, deps: res.deps || [], dynamicDeps: res.dynamicDeps || [] }
+}
+
+async function transformRequestRecursive (viteServer: vite.ViteDevServer, id, parent = '<entry>', chunks: Record<string, TransformChunk> = {}) {
+  if (chunks[id]) {
+    chunks[id].parents.push(parent)
+    return
+  }
+  const res = await transformRequest(viteServer, id)
+  const deps = uniq([...res.deps, ...res.dynamicDeps])
+
+  chunks[id] = {
+    id,
+    code: res.code,
+    deps,
+    parents: [parent]
+  } as TransformChunk
+  for (const dep of deps) {
+    await transformRequestRecursive(viteServer, dep, id, chunks)
+  }
+  return Object.values(chunks)
+}
+
+export async function bundleRequest (viteServer: vite.ViteDevServer, entryURL: string) {
+  const chunks = await transformRequestRecursive(viteServer, entryURL)
+
+  const listIds = (ids: string[]) => ids.map(id => `// - ${id} (${hashId(id)})`).join('\n')
+  const chunksCode = chunks.map(chunk => `
+// --------------------
+// Request: ${chunk.id}
+// Parents: \n${listIds(chunk.parents)}
+// Dependencies: \n${listIds(chunk.deps)}
+// --------------------
+const ${hashId(chunk.id)} = ${chunk.code}
+`).join('\n')
+
+  const manifestCode = 'const __modules__ = {\n' +
+    chunks.map(chunk => ` '${chunk.id}': ${hashId(chunk.id)}`).join(',\n') + '\n}'
+
+  // https://github.com/vitejs/vite/blob/main/packages/vite/src/node/ssr/ssrModuleLoader.ts
+  const ssrModuleLoader = `
+const __pendingModules__ = new Map()
+const __pendingImports__ = new Map()
+const __ssrContext__ = { global: {} }
+
+function __ssrLoadModule__(url, urlStack = []) {
+  const pendingModule = __pendingModules__.get(url)
+  if (pendingModule) { return pendingModule }
+  const modulePromise = __instantiateModule__(url, urlStack)
+  __pendingModules__.set(url, modulePromise)
+  modulePromise.catch(() => { __pendingModules__.delete(url) })
+         .finally(() => { __pendingModules__.delete(url) })
+  return modulePromise
+}
+
+function __createCJSModule__(exports) {
+  return { 
+    get exports() {
+      if (!exports.default)
+        exports.default = {}
+      return exports.default
+    },
+    set exports(v) {
+      exports.default = v
+    }
+  }
+}
+
+async function __instantiateModule__(url, urlStack) {
+  const mod = __modules__[url]
+  if (mod.stubModule) { return mod.stubModule }
+  let stubModule = { [Symbol.toStringTag]: 'Module' }
+  Object.defineProperty(stubModule, '__esModule', { value: true })
+  mod.stubModule = stubModule
+  const importMeta = { url, hot: { accept() {} } }
+  urlStack = urlStack.concat(url)
+  const isCircular = url => urlStack.includes(url)
+  const pendingDeps = []
+  const ssrImport = async (dep) => {
+    // TODO: Handle externals if dep[0] !== '.' | '/'
+    if (!isCircular(dep) && !__pendingImports__.get(dep)?.some(isCircular)) {
+      pendingDeps.push(dep)
+      if (pendingDeps.length === 1) {
+        __pendingImports__.set(url, pendingDeps)
+      }
+      await __ssrLoadModule__(dep, urlStack)
+      if (pendingDeps.length === 1) {
+        __pendingImports__.delete(url)
+      } else {
+        pendingDeps.splice(pendingDeps.indexOf(dep), 1)
+      }
+    }
+    return __modules__[dep].stubModule
+  }
+  function ssrDynamicImport (dep) {
+    // TODO: Handle dynamic import starting with . relative to url
+    return ssrImport(dep)
+  }
+
+  function ssrExportAll(sourceModule) {
+    for (const key in sourceModule) {
+      if (key !== 'default') {
+        try {
+          Object.defineProperty(stubModule, key, {
+            enumerable: true,
+            configurable: true,
+            get() { return sourceModule[key] }
+          })
+        } catch (_err) { }
+      }
+    }
+  }
+
+  await mod(
+    __ssrContext__.global,
+    stubModule,
+    importMeta,
+    ssrImport,
+    ssrDynamicImport,
+    ssrExportAll
+  )
+
+  // fix for cjs/esm misalignment
+  if (!('default' in stubModule)) {
+    stubModule.default = stubModule
+  }
+
+  return stubModule
+}
+`
+
+  const code = [
+    chunksCode,
+    manifestCode,
+    ssrModuleLoader,
+    `module.exports = function (...args) { return __ssrLoadModule__('${entryURL}').then(i => i.default(...args)) }`
+  ].join('\n\n')
+
+  return { code }
+}
diff --git a/src/server.ts b/src/server.ts
index 9ffeb5b..98cc18b 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -1,4 +1,3 @@
-import { builtinModules } from 'module'
 import { resolve } from 'pathe'
 import * as vite from 'vite'
 import { createVuePlugin } from 'vite-plugin-vue2'
@@ -9,7 +8,7 @@ import { ViteBuildContext, ViteOptions } from './types'
 import { wpfs } from './utils/wpfs'
 import { jsxPlugin } from './plugins/jsx'
 import { generateDevSSRManifest } from './manifest'
-import { uniq, hashId } from './utils'
+import { bundleRequest } from './dev-bundler'
 
 export async function buildServer (ctx: ViteBuildContext) {
   // Workaround to disable HMR
@@ -113,152 +112,3 @@ export async function buildServer (ctx: ViteBuildContext) {
     doBuild()
   })
 }
-
-// ---- Vite Dev Bundler POC ----
-
-interface TransformChunk {
-  id: string,
-  code: string,
-  deps: string[],
-  parents: string[]
-}
-
-interface SSRTransformResult {
-  code: string,
-  map: object,
-  deps: string[]
-  dynamicDeps: string[]
-}
-
-async function transformRequest (viteServer: vite.ViteDevServer, id) {
-  // Virtual modules start with `\0`
-  if (id && id.startsWith('/@id/__x00__')) {
-    id = '\0' + id.slice('/@id/__x00__'.length)
-  }
-
-  if (id && id.startsWith('/@id/defaultexport')) {
-    id = id.slice('/@id/'.length)
-  }
-
-  // Externals
-  if (builtinModules.includes(id)) {
-    return {
-      code: `() => require('${id}')`,
-      deps: [],
-      dynamicDeps: []
-    }
-  }
-
-  // Transform
-  const res: SSRTransformResult = await viteServer.transformRequest(id, { ssr: true }).catch((err) => {
-    // eslint-disable-next-line no-console
-    console.warn(`[SSR] Error transforming ${id}: ${err}`)
-    // console.error(err)
-  }) as SSRTransformResult || { code: '', map: {}, deps: [], dynamicDeps: [] }
-
-  // Wrap into a vite module
-  const code = `async function () {
-const exports = {}
-const module = { exports }
-const __vite_ssr_exports__ = exports;
-const __vite_ssr_exportAll__ = __createViteSSRExportAll__(__vite_ssr_exports__)
-${res.code || '/* empty */'};
-return module.exports;
-}`
-  return { code, deps: res.deps || [], dynamicDeps: res.dynamicDeps || [] }
-}
-
-async function transformRequestRecursive (viteServer: vite.ViteDevServer, id, parent = '<entry>', chunks: Record<string, TransformChunk> = {}) {
-  if (chunks[id]) {
-    chunks[id].parents.push(parent)
-    return
-  }
-  const res = await transformRequest(viteServer, id)
-  const deps = uniq([...res.deps, ...res.dynamicDeps])
-
-  chunks[id] = {
-    id,
-    code: res.code,
-    deps,
-    parents: [parent]
-  } as TransformChunk
-  for (const dep of deps) {
-    await transformRequestRecursive(viteServer, dep, id, chunks)
-  }
-  return Object.values(chunks)
-}
-
-async function bundleRequest (viteServer: vite.ViteDevServer, id) {
-  const chunks = await transformRequestRecursive(viteServer, id)
-
-  const listIds = ids => ids.map(id => `// - ${id} (${hashId(id)})`).join('\n')
-  const chunksCode = chunks.map(chunk => `
-// --------------------
-// Request: ${chunk.id}
-// Parents: \n${listIds(chunk.parents)}
-// Dependencies: \n${listIds(chunk.deps)}
-// --------------------
-const ${hashId(chunk.id)} = ${chunk.code}
-`).join('\n')
-
-  const manifestCode = 'const $chunks = {\n' +
-   chunks.map(chunk => ` '${chunk.id}': ${hashId(chunk.id)}`).join(',\n') + '\n}'
-
-  const dynamicImportCode = `
-const __vite_import_cache__ = Object.create({})
-function __vite_ssr_import__(id) {
-  if (!__vite_import_cache__[id]) {
-    __vite_import_cache__[id] = Promise.resolve($chunks[id]())
-      .then(mod => {
-        if (mod && !('default' in mod)) {
-          mod.default = mod
-        }
-        return mod
-      })
-  }
-  return __vite_import_cache__[id]
-}
-function __vite_ssr_dynamic_import__(id) {
-  return __vite_ssr_import__(id)
-}
-`
-
-  // https://github.com/vitejs/vite/blob/fb406ce4c0fe6da3333c9d1c00477b2880d46352/packages/vite/src/node/ssr/ssrModuleLoader.ts#L121-L133
-  const helpers = `
-function __createViteSSRExportAll__(ssrModule) {
-  return (sourceModule) => {
-    for (const key in sourceModule) {
-      if (key !== 'default') {
-        Object.defineProperty(ssrModule, key, {
-          enumerable: true,
-          configurable: true,
-          get() {
-            return sourceModule[key]
-          }
-        })
-      }
-    }
-  }
-}
-`
-
-  // TODO: implement real HMR
-  const metaPolyfill = `
-const __vite_ssr_import_meta__ = {
-  hot: {
-    accept() {}
-  }
-}
-`
-
-  const code = [
-    metaPolyfill,
-    chunksCode,
-    manifestCode,
-    dynamicImportCode,
-    helpers,
-    `module.exports = function (...args) { return ${hashId(id)}().then(r => r.default(...args)) }`
-  ].join('\n\n')
-
-  return { code }
-}