handle rxjs-style observables with get_store_value - fixes #3153

src/runtime/internal/ssr.ts

@@ -114,9 +114,15 @@ export function create_ssr_component(fn) {
 	};
 }
 
+/**
+ * Get the current value from a store by subscribing and immediately unsubscribing.
+ * @param store readable
+ */
 export function get_store_value<T>(store: Readable<T>): T | undefined {
 	let value;
-	store.subscribe(_ => value = _)();
+	const unsubscribe: any = store.subscribe(_ => value = _);
+	if (unsubscribe.unsubscribe) unsubscribe.unsubscribe();
+	else unsubscribe();
 	return value;
 }
 

src/runtime/store/index.ts

@@ -1,4 +1,5 @@
 import { run_all, noop, safe_not_equal, is_function } from 'svelte/internal';
+export { get_store_value as get } from 'svelte/internal';
 
 /** Callback to inform of a value updates. */
 type Subscriber<T> = (value: T) => void;
@@ -188,14 +189,4 @@ export function derived<T, S extends Stores>(
 			};
 		}
 	};
-}
-
-/**
- * Get the current value from a store by subscribing and immediately unsubscribing.
- * @param store readable
- */
-export function get<T>(store: Readable<T>): T {
-	let value: T | undefined;
-	store.subscribe((_: T) => value = _)();
-	return value as T;
-}
+}

test/store/index.ts

@@ -329,5 +329,18 @@ describe('store', () => {
 			const store = readable(42, () => { });
 			assert.equal(get(store), 42);
 		});
+
+		it('works with RxJS-style observables', () => {
+			const observable = {
+				subscribe(fn) {
+					fn(42);
+					return {
+						unsubscribe: () => {}
+					}
+				}
+			};
+
+			assert.equal(get(observable), 42);
+		});
 	});
 });