fix(compiler-sfc): allow `<script>` with lang='js' (#7398)

packages/compiler-sfc/__tests__/__snapshots__/compileScript.spec.ts.snap

@@ -1277,6 +1277,21 @@ return () => {}
 }"
 `;
 
+exports[`SFC compile <script setup> > should compile JS syntax 1`] = `
+"const a = 1
+      const b = 2
+      
+export default {
+  setup(__props, { expose }) {
+  expose();
+
+      
+return { a, b }
+}
+
+}"
+`;
+
 exports[`SFC compile <script setup> > should expose top level declarations 1`] = `
 "import { x } from './x'
       

packages/compiler-sfc/__tests__/compileScript.spec.ts

@@ -2,6 +2,17 @@ import { BindingTypes } from '@vue/compiler-core'
 import { compileSFCScript as compile, assertCode, mockId } from './utils'
 
 describe('SFC compile <script setup>', () => {
+  test('should compile JS syntax', () => {
+    const { content } = compile(`
+      <script setup lang='js'>
+      const a = 1
+      const b = 2
+      </script>
+    `)
+    expect(content).toMatch(`return { a, b }`)
+    assertCode(content)
+  })
+
   test('should expose top level declarations', () => {
     const { content, bindings } = compile(`
       <script setup>

packages/compiler-sfc/src/compileScript.ts

@@ -167,6 +167,11 @@ export function compileScript(
   const cssVars = sfc.cssVars
   const scriptLang = script && script.lang
   const scriptSetupLang = scriptSetup && scriptSetup.lang
+  const isJS =
+    scriptLang === 'js' ||
+    scriptLang === 'jsx' ||
+    scriptSetupLang === 'js' ||
+    scriptSetupLang === 'jsx'
   const isTS =
     scriptLang === 'ts' ||
     scriptLang === 'tsx' ||
@@ -196,7 +201,7 @@ export function compileScript(
     if (!script) {
       throw new Error(`[@vue/compiler-sfc] SFC contains no <script> tags.`)
     }
-    if (scriptLang && !isTS && scriptLang !== 'jsx') {
+    if (scriptLang && !isJS && !isTS) {
       // do not process non js/ts script blocks
       return script
     }
@@ -264,7 +269,7 @@ export function compileScript(
     )
   }
 
-  if (scriptSetupLang && !isTS && scriptSetupLang !== 'jsx') {
+  if (scriptSetupLang && !isJS && !isTS) {
     // do not process non js/ts script blocks
     return scriptSetup
   }