Adds SyncScheduler.

This is a `Scheduler` implementation which immediately invokes any scheduled action synchronously. I'm not 100% this is a good idea at this stage, but the current expected use is for one component to synchronously communicate changes another so DOM operations across all of them can be batched together in a single async task scheduled via `setTimeout` / `requestAnimationFrame`. If each component used `setTimeout`, then each component's DOM operaitons would be independently scheduled one macrotask apart from each other and result in unnecessary DOM thrashing.
dgp1130 · Dec 2, 2024 · 5dd1efc · 5dd1efc
1 parent 703b743
commit 5dd1efc
Show file tree

Hide file tree

Showing 3 changed files with 45 additions and 0 deletions.
diff --git a/src/signals/schedulers/sync-scheduler.test.html b/src/signals/schedulers/sync-scheduler.test.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>`sync-scheduler` tests</title>
+        <meta charset="utf8">
+    </head>
+    <body></body>
+</html>
diff --git a/src/signals/schedulers/sync-scheduler.test.ts b/src/signals/schedulers/sync-scheduler.test.ts
@@ -0,0 +1,22 @@
+import { Action } from './scheduler.js';
+import { syncScheduler } from './sync-scheduler.js';
+
+describe('sync-scheduler', () => {
+  describe('SyncScheduler', () => {
+    describe('schedule', () => {
+      it('executes the given action synchronously', () => {
+        const action = jasmine.createSpy<Action>('action');
+
+        syncScheduler.schedule(action);
+        expect(action).toHaveBeenCalledOnceWith();
+      });
+
+      it('ignores cancel operations', () => {
+        const action = jasmine.createSpy<Action>('action');
+
+        const cancel = syncScheduler.schedule(action);
+        expect(cancel).not.toThrow();
+      });
+    });
+  });
+});
diff --git a/src/signals/schedulers/sync-scheduler.ts b/src/signals/schedulers/sync-scheduler.ts
@@ -0,0 +1,15 @@
+import { Action, CancelAction, Scheduler } from './scheduler.js';
+
+/**
+ * A {@link Scheduler} implementation which always executes operations
+ * synchronously, immediately when scheduled.
+ */
+class SyncScheduler implements Scheduler {
+  public schedule(action: Action): CancelAction {
+    action();
+    return () => {};
+  }
+}
+
+/** Singleton {@link SyncScheduler} for shared usage. */
+export const syncScheduler = new SyncScheduler();