save code when it's there

src/hooks/useSaveSignupCodeToLocalStorage.ts

@@ -0,0 +1,14 @@
+import { useSearchParams } from 'react-router-dom'
+import { useEffect } from 'react'
+
+export function useSaveSignupCodeToLocalStorage() {
+  const [searchParams] = useSearchParams()
+
+  const code = searchParams.get('ck')
+
+  useEffect(() => {
+    if (code) {
+      localStorage.setItem('signupCode', code)
+    }
+  }, [code])
+}