SvelteKit will skip generating types if it cannot detect TypeScript environment. Therefore this ad-hoc script is born.

sync.js

import child_process from 'node:child_process'

function run(cmd) {
  child_process.execSync(cmd, { stdio: 'inherit' })
}

;(async () => {
  let ts_patched = false

  try {
    await import('typescript')
  } catch (err) {
    console.log('Typescript not detected. Installing...')
    run('npm i typescript -D')
    ts_patched = true
  }

  console.log('Running sync...')
  run('npx --yes svelte-kit sync')

  if (ts_patched) {
    console.log('Removing typescript...')
    run('npm r typescript')
  }

})()