tauri-workspace/core/tests/uninitialized-ipc/index.html

<script>
  const exit = (code) => window.__TAURI_INVOKE__('exit', { code })
  window.addEventListener('message', ({ data }) => {
    console.log(data)
    switch (data) {
      case 'undefined':
        exit(0)
        break
      case 'function':
        exit(1)
        break
      default:
        exit(2)
    }
  })
</script>
<iframe src="uninitialized://localhost/"></iframe>