Add Svelte async hook

ts/graphs/async.ts

@@ -0,0 +1,28 @@
+import { Readable, readable, derived } from "svelte/store";
+
+interface AsyncData<T, E> {
+    value: Readable<T | null>,
+    error: Readable<E | null>,
+    pending: Readable<boolean>,
+    successful: Readable<boolean>,
+}
+
+
+function useAsync<T, E = Error>(asyncFunction: () => Promise<T>): AsyncData<T, E> {
+    const promise = asyncFunction();
+
+    const value = readable(null, (set: (value: T) => void) => {
+        promise.then((value: T) => set(value))
+    })
+
+    const error = readable(null, (set: (value: E) => void) => {
+        promise.catch((value: E) => set(value))
+    })
+
+    const pending = derived([value, error], (_, set) => set(true), true)
+    const successful = derived([value], (_, set) => set(true), false)
+
+    return { value, error, pending, successful }
+}
+
+export default useAsync