Add files

src/helper/wait-while-false.ts

@@ -0,0 +1,29 @@
+export const waitWhileFalse = (body: () => boolean): Promise<void> => {
+  let resolveOnDone: () => void;
+  let rejectOnDone: (e: Error) => void;
+
+  const onDone = new Promise<void>((resolve, reject) => {
+    resolveOnDone = resolve;
+    rejectOnDone = reject;
+  });
+
+  const waiter = () => {
+    let success: boolean;
+
+    try {
+      success = body();
+    } catch (e) {
+      rejectOnDone(e);
+      return;
+    }
+
+    if (success) {
+      resolveOnDone();
+    } else {
+      requestAnimationFrame(waiter);
+    }
+  };
+
+  waiter();
+  return onDone;
+};