swiper/core/update/updateSlidesOffset.js

export default function updateSlidesOffset() {
  const swiper = this;
  const slides = swiper.slides;

  for (let i = 0; i < slides.length; i += 1) {
    slides[i].swiperSlideOffset = swiper.isHorizontal() ? slides[i].offsetLeft : slides[i].offsetTop;
  }
}