Migrate typing util to TypeScript

src/util/typing.js → src/util/typing.ts

@@ -1,7 +1,4 @@
-/**
- * @template T
- * @typedef {import('preact').Ref<T>} Ref
- */
+import type { Ref } from 'preact';
 
 /**
  * Helper for downcasting a ref to a more specific type, where that is safe
@@ -10,12 +7,7 @@
  * This is mainly useful to cast a generic `Ref<HTMLElement>` to a more specific
  * element type (eg. `Ref<HTMLDivElement>`) for use with the `ref` prop of a JSX element.
  * Since Preact only writes to the `ref` prop, such a cast is safe.
- *
- * @template T
- * @template {T} U
- * @param {Ref<T>|undefined} ref
- * @return {Ref<U>|undefined}
  */
-export function downcastRef(ref) {
-  return /** @type {Ref<U>|undefined} */ (ref);
+export function downcastRef<T, U>(ref: Ref<T> | undefined): Ref<U> | undefined {
+  return ref as Ref<U> | undefined;
 }