Migrate Idler

Summary: _typescript_

Reviewed By: danielbuechele

Differential Revision: D16763946

fbshipit-source-id: 96eb0cdaca8a6cd731a6d16f3bea02471c691c01

src/utils/Idler.tsx

@@ -0,0 +1,36 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import {CancelledPromiseError} from './errors';
+
+export class Idler {
+  lastIdle: number;
+  interval: number;
+  kill: boolean;
+
+  constructor() {
+    this.lastIdle = 0;
+    this.interval = 3;
+    this.kill = false;
+  }
+
+  idle(): Promise<void> {
+    if (this.kill) {
+      throw new CancelledPromiseError('Idler got killed');
+    }
+    const now = performance.now();
+    if (now - this.lastIdle > this.interval) {
+      this.lastIdle = now;
+      return new Promise(resolve => setTimeout(resolve, 0));
+    }
+    return Promise.resolve();
+  }
+
+  cancel() {
+    this.kill = true;
+  }
+}