feat: enable generatedCode: 'es2015' for rollup build (#5018)

Co-authored-by: sapphi-red <green@sapphi.red>

Author: antfu

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

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";)(.*)/
 

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 () => {