Add promiseStore to easily wrap a Promise as a store. Useful for Svel…

…teKit streamed data handling

.changeset/twenty-paws-play.md

@@ -0,0 +1,5 @@
+---
+'svelte-ux': patch
+---
+
+Add promiseStore to easily wrap a Promise as a store. Useful for SvelteKit streamed data handling

src/lib/stores/index.ts

@@ -8,6 +8,7 @@ export { default as localStore } from './localStore';
 export { default as mapStore } from './mapStore';
 export * from './matchMedia';
 export { default as paginationStore } from './paginationStore';
+export * from './promiseStore';
 export { default as selectionStore } from './selectionStore';
 export { default as tableOrderStore } from './tableOrderStore';
 export { default as timerStore } from './timerStore';

src/lib/stores/promiseStore.ts

@@ -0,0 +1,65 @@
+import { writable } from 'svelte/store';
+
+export type PromiseStoreData<T> = {
+  loading: boolean;
+  data?: T;
+  error?: Error;
+  aborted?: boolean;
+};
+
+const WAITING = Symbol();
+
+/**
+ * Add promiseStore to easily wrap a Promise as a store.  Useful for SvelteKit streamed data handling
+ */
+export function promiseStore<T>(initialValue?: Promise<T> | null) {
+  let currentPromise: Promise<T> | null = null;
+
+  let store = writable<PromiseStoreData<T>>({
+    loading: false,
+    aborted: false,
+  });
+
+  let result = {
+    subscribe: store.subscribe,
+
+    async setPromise(promise: Promise<T> | undefined) {
+      if (!promise) {
+        currentPromise = null;
+        store.set({
+          data: undefined,
+          loading: false,
+          aborted: false,
+        });
+        return;
+      }
+
+      // If promise is already resolved, update immediately
+      const resolved = await Promise.race([promise, Promise.resolve(WAITING)]);
+      if (resolved === WAITING) {
+        store.update((s) => ({ ...s, loading: true }));
+      }
+
+      if (promise !== currentPromise) {
+        currentPromise = promise;
+        try {
+          const data = await promise;
+          if (currentPromise === promise) {
+            store.set({ data, loading: false, aborted: false });
+          }
+        } catch (err) {
+          if (currentPromise === promise) {
+            const error = err as Error;
+            store.set({ error, aborted: error.name === 'AbortError', loading: false });
+          }
+        }
+      }
+    },
+  };
+
+  if (initialValue) {
+    result.setPromise(initialValue);
+  }
+
+  return result;
+}