import { animate, utils, stagger } from 'animejs';

const [ $completeButton ] = utils.$('.complete');

const animation = animate('.square', {
  x: '17rem',
  alternate: true,
  ease: 'inOutSine',
  loop: true,
  delay: stagger(100),
});

const completeAnimation = () => animation.complete();

$completeButton.addEventListener('click', completeAnimation);

<div class="medium row">
  <div class="square"></div>
</div>
<div class="medium row">
  <div class="square"></div>
</div>
<div class="medium row">
  <fieldset class="controls">
    <button class="button complete">Complete</button>
  </fieldset>
</div>