Staggered nudge. wave reveal

startDelay is the sugar for a wave-style reveal. Every reel’s tween starts at a different time but runs concurrently. sharper than a sequential await loop (no reel waits for the previous to fully land), more readable than a fully synchronised parallel (the eye can follow the wave reel by reel).

The pattern

const NUDGE_COLS = [0, 1, 2, 3, 4];
const NUDGE_DURATION = 520;
const STAGGER_MS = 90;

await Promise.all(
  NUDGE_COLS.map((col, i) =>
    reelSet.nudge(col, {
      distance: 1,
      direction: 'down',
      incoming: ['wild'],
      duration: NUDGE_DURATION,
      startDelay: i * STAGGER_MS,
    }),
  ),
);

Total wall time:

For 5 reels × 520 ms duration × 90 ms stagger that’s 4 * 90 + 520 = 880 ms total. Each reel’s tween still runs its full 520 ms. just spread across the window.

Irregular stagger profiles

For ease-style stagger curves (faster start, slower end), just compute per-reel delays explicitly:

const delays = [0, 50, 110, 180, 260]; // accelerating wave
await Promise.all(
  cols.map((col, i) =>
    reelSet.nudge(col, { ...opts, startDelay: delays[i] }),
  ),
);

Validation throws still fire synchronously

startDelay only defers the strip mutation + tween. Argument-shape errors (distance out of range, unknown incoming id, pin overlap on the target reel) still throw on the call site:

// Throws immediately even though startDelay=1000 was passed.
await reelSet.nudge(2, {
  distance: 0,             // invalid
  direction: 'down',
  incoming: [],
  startDelay: 1000,
});

This keeps “where did the error come from” debuggable. Errors don’t get laundered into a delayed rejection a second later.

Cancelling a staggered wave mid-flight

Pass the same AbortSignal to every call and reels whose tween hasn’t started yet bail before mutating anything; reels already mid-tween snap to landed and reject with AbortError. See Abort a nudge.

Related

• Nudge a reel. sequential / parallel / now stagger.
• Spotlight after a nudge. pair with WinPresenter.