Wrapper around requestIdleCallback to wait for a minimum work budget

on-idle.js

/**
 * Delays calling the given function until the browser is notifying us
 * about a certain minimum budget or the timeout is reached.
 * @param {!Window} win
 * @param {number} startTime When we started waiting for idle.
 * @param {number} minimumTimeRemaining Minimum number of millis idle
 *     budget for callback to fire.
 * @param {number} timeout in millis for callback to fire.
 * @param {function()} fn Callback.
 */
export function onIdle(win, startTime, minimumTimeRemaining, timeout, fn) {
  win.requestIdleCallback(info => {
    if (info.timeRemaining() < minimumTimeRemaining) {
      const now = Date.now();
      const remainingTimeout = timeout - (now - startTime);
      if (remainingTimeout <= 0 || info.didTimeout) {
        fn();
      } else {
        onIdle(win, now, minimumTimeRemaining, remainingTimeout, fn);
      }
    } else {
      fn();
    }
  }, {
    timeout: timeout,
  });
}