Repro: Multiple export default in <script> — JS throws, TS does not

This repository is a minimal repro for filing an issue to Vue Core, focusing on an inconsistency when a single SFC <script> contains multiple export default declarations: JavaScript throws, TypeScript does not.

• Related query: https://github.com/vuejs/core/issues?q=script%20multiple%20export%20default%20error

Problem Statement

• In plain JavaScript SFCs, vue/compiler-sfc throws a syntax error: only one default export is allowed per module.
• In TypeScript SFCs (<script lang="ts">), compileScript returns content that still contains two export default blocks without throwing, which differs from JS behavior.

Repository Layout

• src/ComponentVanilla.vue: JS variant with two export default declarations
• src/ComponentTS.vue: TS variant (<script lang="ts">) with two export default declarations
• compile.ts: uses vue/compiler-sfc parse + compileScript to compile and log results
• compileJavascriptCode.ts: runs compilation for the JS component
• compileTypescriptCode.ts: runs compilation for the TS component

Requirements

• Node.js ≥ 18 (verified with v22)
• Package manager: yarn or npm

Install

• yarn install or
• npm install

Reproduce

1. JS repro

   • Command: npx tsx compileJavascriptCode.ts
   • Expected: throws duplicate default export error
     • Example: Only one default export allowed per module. (DuplicateDefaultExport)
     • Also prints target lang js

2. TS repro

   • Command: npx tsx compileTypescriptCode.ts
   • Expected: does not throw; prints the compiled content
     • Logs lang-> ts
     • Logs content-> followed by the two export default blocks

Sample Output

• JS (src/ComponentVanilla.vue):

  • error SyntaxError: [vue/compiler-sfc] Only one default export allowed per module.
  • reasonCode: 'DuplicateDefaultExport'
  • target lang js

• TS (src/ComponentTS.vue):

  • lang-> ts
  • content-> shows two export default {...} blocks; no error

Expected vs Actual

• Expected: TypeScript and JavaScript should be consistent and both report an error when multiple export default are present in the same module.
• Actual: JS errors; TS does not. The discrepancy warrants discussion and alignment in Vue Core.

Notes

• To keep things simple, this repro uses npx tsx to run the TypeScript driver files directly; no additional build setup is required.