swiper/core/transition/transitionStart.js

import transitionEmit from './transitionEmit.js';
export default function transitionStart(runCallbacks = true, direction) {
  const swiper = this;
  const {
    params
  } = swiper;
  if (params.cssMode) return;

  if (params.autoHeight) {
    swiper.updateAutoHeight();
  }

  transitionEmit({
    swiper,
    runCallbacks,
    direction,
    step: 'Start'
  });
}