Improve scheduling of requestIdleCallback tasks (#3477)

app/javascript/mastodon/features/ui/util/schedule_idle_task.js

@@ -0,0 +1,29 @@
+// Wrapper to call requestIdleCallback() to schedule low-priority work.
+// See https://developer.mozilla.org/en-US/docs/Web/API/Background_Tasks_API
+// for a good breakdown of the concepts behind this.
+
+import Queue from 'tiny-queue';
+
+const taskQueue = new Queue();
+let runningRequestIdleCallback = false;
+
+function runTasks(deadline) {
+  while (taskQueue.length && deadline.timeRemaining() > 0) {
+    taskQueue.shift()();
+  }
+  if (taskQueue.length) {
+    requestIdleCallback(runTasks);
+  } else {
+    runningRequestIdleCallback = false;
+  }
+}
+
+function scheduleIdleTask(task) {
+  taskQueue.push(task);
+  if (!runningRequestIdleCallback) {
+    runningRequestIdleCallback = true;
+    requestIdleCallback(runTasks);
+  }
+}
+
+export default scheduleIdleTask;