runTaskQueue.js

  // requestIdleCallback's callback.
  runTaskQueue(deadline) {
    console.info(`This round of JS begins at ${this.currentTaskNumber}.`);
    while (deadline.timeRemaining() > 0 && this.taskList.length) {
      // deadline.timeRemaining() runs repeatedly, until it is equal
      // to 0. It slowly decreases... 12.465 -> 11.26 -> etc.
      const task = this.taskList.shift();
      this.currentTaskNumber++;

      // This creates the DOM elements but does not log them.
      task.handler(task.data);
      // This adds the created elements to the DOM with requestAnimationFrame.
      this.scheduleStatusRefresh();
    }
    console.info(`And ends at ${this.currentTaskNumber}.`);
    // Then run the next task.
    if (this.taskList.length) {
      this.taskHandle = requestIdleCallback(this.runTaskQueue);
    } else {
      this.taskHandle = 0;
    }
  }