swiper/src/components/core/transition/transitionStart.js

Most modern mobile touch slider and framework with hardware accelerated transitions

export default function (runCallbacks = true, direction) {
  const swiper = this;
  const { activeIndex, params, previousIndex } = swiper;
  if (params.cssMode) return;
  if (params.autoHeight) {
    swiper.updateAutoHeight();
  }

  let dir = direction;
  if (!dir) {
    if (activeIndex > previousIndex) dir = 'next';
    else if (activeIndex < previousIndex) dir = 'prev';
    else dir = 'reset';
  }

  swiper.emit('transitionStart');

  if (runCallbacks && activeIndex !== previousIndex) {
    if (dir === 'reset') {
      swiper.emit('slideResetTransitionStart');
      return;
    }
    swiper.emit('slideChangeTransitionStart');
    if (dir === 'next') {
      swiper.emit('slideNextTransitionStart');
    } else {
      swiper.emit('slidePrevTransitionStart');
    }
  }
}