diff --git a/packages/vite/src/node/__tests__/build.spec.ts b/packages/vite/src/node/__tests__/build.spec.ts
index a61db117e81112..915c2c5392d526 100644
--- a/packages/vite/src/node/__tests__/build.spec.ts
+++ b/packages/vite/src/node/__tests__/build.spec.ts
@@ -182,9 +182,9 @@ describe('resolveBuildOutputs', () => {
       {
         format: 'es',
       },
-      // {
-      //   format: 'umd',
-      // },
+      {
+        format: 'umd',
+      },
     ])
   })
 
@@ -223,7 +223,7 @@ describe('resolveBuildOutputs', () => {
     expect(resolveBuild).toThrowError(/Option "build\.lib\.name" is required/)
   })
 
-  test.skip('throws an error when lib.name is missing on umd format', () => {
+  test('throws an error when lib.name is missing on umd format', () => {
     const logger = createLogger()
     const libOptions: LibraryOptions = { ...baseLibOptions, formats: ['umd'] }
     const resolveBuild = () => resolveBuildOutputs(void 0, libOptions, logger)
@@ -242,7 +242,7 @@ describe('resolveBuildOutputs', () => {
     )
   })
 
-  test.skip('throws an error when output.name is missing on umd format', () => {
+  test('throws an error when output.name is missing on umd format', () => {
     const logger = createLogger()
     const libOptions: LibraryOptions = { ...baseLibOptions }
     const outputs: OutputOptions[] = [{ format: 'umd' }]
@@ -346,7 +346,7 @@ describe('resolveLibFilename', () => {
   test('module package extensions', () => {
     const formatsToFilenames: FormatsToFileNames = [
       ['es', 'my-lib.js'],
-      // ['umd', 'my-lib.umd.cjs'],
+      ['umd', 'my-lib.umd.cjs'],
       ['cjs', 'my-lib.cjs'],
       ['iife', 'my-lib.iife.js'],
     ]
@@ -496,13 +496,13 @@ describe('resolveBuildOutputs', () => {
 
     expect(resolveBuildOutputs(undefined, libOptions, {} as Logger)).toEqual([
       { format: 'es' },
-      // { format: 'umd' },
+      { format: 'umd' },
     ])
     expect(
       resolveBuildOutputs({ name: 'A' }, libOptions, {} as Logger),
     ).toEqual([
       { format: 'es', name: 'A' },
-      // { format: 'umd', name: 'A' },
+      { format: 'umd', name: 'A' },
     ])
     expect(
       resolveBuildOutputs([{ name: 'A' }], libOptions, {} as Logger),
@@ -529,7 +529,7 @@ describe('resolveBuildOutputs', () => {
     ).toEqual([{ name: 'A' }])
   })
 
-  test.skip('umd or iife: should not support multiple entries', () => {
+  test('umd or iife: should not support multiple entries', () => {
     ;['umd', 'iife'].forEach((format) => {
       expect(() =>
         resolveBuildOutputs(
@@ -546,7 +546,7 @@ describe('resolveBuildOutputs', () => {
     })
   })
 
-  test.skip('umd or iife: should define build.lib.name', () => {
+  test('umd or iife: should define build.lib.name', () => {
     ;['umd', 'iife'].forEach((format) => {
       expect(() =>
         resolveBuildOutputs(
diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index d6665884233256..f6a133bed15d3c 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -314,7 +314,7 @@ export interface LibraryOptions {
   cssFileName?: string
 }
 
-export type LibraryFormats = 'es' | 'cjs' | 'iife' // | 'umd' | 'system'
+export type LibraryFormats = 'es' | 'cjs' | 'iife' | 'umd' // | 'system'
 
 export interface ModulePreloadOptions {
   /**
@@ -773,7 +773,7 @@ async function buildEnvironment(
           ? `[name].[ext]`
           : path.posix.join(options.assetsDir, `[name]-[hash].[ext]`),
         inlineDynamicImports:
-          /* output.format === 'umd' || */ output.format === 'iife',
+          output.format === 'umd' || output.format === 'iife',
         ...output,
       }
     }
@@ -931,7 +931,7 @@ function resolveOutputJsExtension(
   type: string = 'commonjs',
 ): JsExt {
   if (type === 'module') {
-    return format === 'cjs' /* || format === 'umd' */ ? 'cjs' : 'js'
+    return format === 'cjs' || format === 'umd' ? 'cjs' : 'js'
   } else {
     return format === 'es' ? 'mjs' : 'js'
   }
@@ -981,10 +981,10 @@ export function resolveBuildOutputs(
       Object.values(libOptions.entry).length > 1
     const libFormats =
       libOptions.formats ||
-      (libHasMultipleEntries ? ['es', 'cjs'] : ['es' /* , 'umd' */])
+      (libHasMultipleEntries ? ['es', 'cjs'] : ['es', 'umd'])
 
     if (!Array.isArray(outputs)) {
-      if (/* libFormats.includes('umd') || */ libFormats.includes('iife')) {
+      if (libFormats.includes('umd') || libFormats.includes('iife')) {
         if (libHasMultipleEntries) {
           throw new Error(
             'Multiple entry points are not supported when output formats include "umd" or "iife".',
@@ -1012,7 +1012,7 @@ export function resolveBuildOutputs(
 
     outputs.forEach((output) => {
       if (
-        /* output.format === 'umd' || */ output.format === 'iife' &&
+        (output.format === 'umd' || output.format === 'iife') &&
         !output.name
       ) {
         throw new Error(
diff --git a/packages/vite/src/node/packages.ts b/packages/vite/src/node/packages.ts
index 6af2f2cb4e55ce..468fc4cbb0595b 100644
--- a/packages/vite/src/node/packages.ts
+++ b/packages/vite/src/node/packages.ts
@@ -272,15 +272,14 @@ export function watchPackageDataPlugin(packageCache: PackageCache): Plugin {
   return {
     name: 'vite:watch-package-data',
     buildStart() {
-      // watchFile = this.addWatchFile.bind(this)
+      watchFile = this.addWatchFile.bind(this)
       watchQueue.forEach(watchFile)
       watchQueue.clear()
     },
     buildEnd() {
       watchFile = watchFileStub
     },
-    // TODO: use watchChange hook when implemented
-    handleHotUpdate({ file: id }) {
+    watchChange(id) {
       if (id.endsWith('/package.json')) {
         invalidatePackageData(packageCache, path.normalize(id))
       }
diff --git a/packages/vite/src/node/plugins/esbuild.ts b/packages/vite/src/node/plugins/esbuild.ts
index 9b8787c8fed4a8..f56a73fd9d745d 100644
--- a/packages/vite/src/node/plugins/esbuild.ts
+++ b/packages/vite/src/node/plugins/esbuild.ts
@@ -356,9 +356,9 @@ export const buildEsbuildPlugin = (config: ResolvedConfig): Plugin => {
         const contentIndex =
           opts.format === 'iife'
             ? Math.max(esbuildCode.search(IIFE_BEGIN_RE), 0)
-            : // : opts.format === 'umd'
-              //   ? esbuildCode.indexOf(`(function(`) // same for minified or not
-              0
+            : opts.format === 'umd'
+              ? esbuildCode.indexOf(`(function(`) // same for minified or not
+              : 0
         if (contentIndex > 0) {
           const esbuildHelpers = esbuildCode.slice(0, contentIndex)
           res.code = esbuildCode
diff --git a/vitest.config.e2e.ts b/vitest.config.e2e.ts
index e7b087d24a1bdc..18685bf4f8d1c2 100644
--- a/vitest.config.e2e.ts
+++ b/vitest.config.e2e.ts
@@ -19,7 +19,6 @@ export default defineConfig({
         ? [
             './playground/environment-react-ssr/**/*.spec.[tj]s', // needs investigation
             './playground/external/**/*.spec.[tj]s', // https://github.com/rolldown/rolldown/issues/2041
-            './playground/lib/**/*.spec.[tj]s', // umd format
             './playground/object-hooks/**/*.spec.[tj]s', // object hook sequential
             './playground/optimize-deps/**/*.spec.[tj]s', // https://github.com/rolldown/rolldown/issues/2031
             './playground/tsconfig-json/__tests__/**/*.spec.[tj]s', // decorators is not supported by oxc