Use POST data in forms in SSR with SolidStart

solid-start-form-post-ssr.tsx

import {isServer} from 'solid-js/web'
import {createRouteData} from 'solid-start'
import {useRequest} from 'solid-start/server'

export default function FormPage() {
  const postData = createRouteData(async () => {
    const event = useRequest()
    if (!isServer || event.request.method !== 'POST') {
      return undefined
    }

    const data = await event.request.formData()
    return Object.fromEntries(data) as Record<string, string>
  })

  return <>
    <h1>SSR-only Form POST data</h1>
    <form method='post' enctype='multipart/form-data'>
      <input type='hidden' name='subject' value={postData()?.subject ?? 'Defense against the Dark Arts'} />
      <input type='text' name='myfield' class='border' value={postData()?.myfield ?? ''} />
      <button type='submit'>Submit</button>
      <pre>{JSON.stringify(postData())}</pre>
    </form>
  </>
}