How to anticipate a reel

The minimum code

const promise = reelSet.spin();

// ...some time later, when the server response arrives:
reelSet.setAnticipation([3, 4]);    // slow the last two reels
reelSet.setResult(response.symbols);

const result = await promise;

Reading the anticipation in progress

Listen to spin:stopping to tell UI state when any reel enters its stop-phase (anticipation counts as part of stopping):

reelSet.events.on('spin:stopping', (reelIndex) => {
  if (anticipationReels.includes(reelIndex)) {
    playTensionSound();
  }
});

Customize the feel

The wait time and easing come from the active SpeedProfile.anticipationDelay. Per-game feel: define a custom profile and switch to it for bonus rounds.

builder.speed('cinematic', {
  ...SpeedPresets.NORMAL,
  anticipationDelay: 1400,
  decelerationEase: 'elastic.out(1, 0.5)',
});