diff --git a/packages/vite/src/node/build.ts b/packages/vite/src/node/build.ts
index 4b26a958939ffa..ea40914fdb44c8 100644
--- a/packages/vite/src/node/build.ts
+++ b/packages/vite/src/node/build.ts
@@ -426,6 +426,7 @@ async function doBuild(
         exports: ssr ? 'named' : 'auto',
         sourcemap: options.sourcemap,
         name: libOptions ? libOptions.name : undefined,
+        generatedCode: 'es2015',
         entryFileNames: ssr
           ? `[name].js`
           : libOptions
diff --git a/packages/vite/src/node/plugins/esbuild.ts b/packages/vite/src/node/plugins/esbuild.ts
index 5250f4baf7687b..7b02af2152cb70 100644
--- a/packages/vite/src/node/plugins/esbuild.ts
+++ b/packages/vite/src/node/plugins/esbuild.ts
@@ -27,7 +27,7 @@ import { searchForWorkspaceRoot } from '..'
 const debug = createDebugger('vite:esbuild')
 
 const INJECT_HELPERS_IIFE_RE =
-  /(.*)(var [^\s]+=function\([^)]*?\){"use strict";)(.*)/
+  /(.*)((?:const|var) [^\s]+=function\([^)]*?\){"use strict";)(.*)/
 const INJECT_HELPERS_UMD_RE =
   /(.*)(\(function\([^)]*?\){.+amd.+function\([^)]*?\){"use strict";)(.*)/
 
diff --git a/playground/lib/__tests__/lib.spec.ts b/playground/lib/__tests__/lib.spec.ts
index c64ccfa075d0e4..f8eea2b41847b8 100644
--- a/playground/lib/__tests__/lib.spec.ts
+++ b/playground/lib/__tests__/lib.spec.ts
@@ -31,7 +31,7 @@ describe.runIf(isBuild)('build', () => {
       'utf-8'
     )
     // esbuild helpers are injected inside of the IIFE wrapper
-    expect(code).toMatch(/^var MyLib=function\(\){"use strict";/)
+    expect(code).toMatch(/^const MyLib=function\(\){"use strict";/)
   })
 
   test('Library mode does not include `preload`', async () => {