swiper/core/loop/loopFix.js

export default function loopFix() {
  const swiper = this;
  swiper.emit('beforeLoopFix');
  const {
    activeIndex,
    slides,
    loopedSlides,
    allowSlidePrev,
    allowSlideNext,
    snapGrid,
    rtlTranslate: rtl
  } = swiper;
  let newIndex;
  swiper.allowSlidePrev = true;
  swiper.allowSlideNext = true;
  const snapTranslate = -snapGrid[activeIndex];
  const diff = snapTranslate - swiper.getTranslate(); // Fix For Negative Oversliding

  if (activeIndex < loopedSlides) {
    newIndex = slides.length - loopedSlides * 3 + activeIndex;
    newIndex += loopedSlides;
    const slideChanged = swiper.slideTo(newIndex, 0, false, true);

    if (slideChanged && diff !== 0) {
      swiper.setTranslate((rtl ? -swiper.translate : swiper.translate) - diff);
    }
  } else if (activeIndex >= slides.length - loopedSlides) {
    // Fix For Positive Oversliding
    newIndex = -slides.length + activeIndex + loopedSlides;
    newIndex += loopedSlides;
    const slideChanged = swiper.slideTo(newIndex, 0, false, true);

    if (slideChanged && diff !== 0) {
      swiper.setTranslate((rtl ? -swiper.translate : swiper.translate) - diff);
    }
  }

  swiper.allowSlidePrev = allowSlidePrev;
  swiper.allowSlideNext = allowSlideNext;
  swiper.emit('loopFix');
}