swiper/src/components/lazy/lazy.js

Most modern mobile touch slider and framework with hardware accelerated transitions

import $ from '../../utils/dom';
import Utils from '../../utils/utils';

const Lazy = {
  loadInSlide(index, loadInDuplicate = true) {
    const swiper = this;
    const params = swiper.params.lazy;
    if (typeof index === 'undefined') return;
    if (swiper.slides.length === 0) return;
    const isVirtual = swiper.virtual && swiper.params.virtual.enabled;

    const $slideEl = isVirtual
      ? swiper.$wrapperEl.children(`.${swiper.params.slideClass}[data-swiper-slide-index="${index}"]`)
      : swiper.slides.eq(index);

    let $images = $slideEl.find(`.${params.elementClass}:not(.${params.loadedClass}):not(.${params.loadingClass})`);
    if ($slideEl.hasClass(params.elementClass) && !$slideEl.hasClass(params.loadedClass) && !$slideEl.hasClass(params.loadingClass)) {
      $images = $images.add($slideEl[0]);
    }
    if ($images.length === 0) return;

    $images.each((imageIndex, imageEl) => {
      const $imageEl = $(imageEl);
      $imageEl.addClass(params.loadingClass);

      const background = $imageEl.attr('data-background');
      const src = $imageEl.attr('data-src');
      const srcset = $imageEl.attr('data-srcset');
      const sizes = $imageEl.attr('data-sizes');
      const $pictureEl = $imageEl.parent('picture');

      swiper.loadImage($imageEl[0], (src || background), srcset, sizes, false, () => {
        if (typeof swiper === 'undefined' || swiper === null || !swiper || (swiper && !swiper.params) || swiper.destroyed) return;
        if (background) {
          $imageEl.css('background-image', `url("${background}")`);
          $imageEl.removeAttr('data-background');
        } else {
          if (srcset) {
            $imageEl.attr('srcset', srcset);
            $imageEl.removeAttr('data-srcset');
          }
          if (sizes) {
            $imageEl.attr('sizes', sizes);
            $imageEl.removeAttr('data-sizes');
          }
          if ($pictureEl.length) {
            $pictureEl.children('source').each((sourceIndex, sourceEl) => {
              const $source = $(sourceEl);

              if ($source.attr('data-srcset')) {
                $source.attr('srcset', $source.attr('data-srcset'));
                $source.removeAttr('data-srcset');
              }
            });
          }
          if (src) {
            $imageEl.attr('src', src);
            $imageEl.removeAttr('data-src');
          }
        }

        $imageEl.addClass(params.loadedClass).removeClass(params.loadingClass);
        $slideEl.find(`.${params.preloaderClass}`).remove();
        if (swiper.params.loop && loadInDuplicate) {
          const slideOriginalIndex = $slideEl.attr('data-swiper-slide-index');
          if ($slideEl.hasClass(swiper.params.slideDuplicateClass)) {
            const originalSlide = swiper.$wrapperEl.children(`[data-swiper-slide-index="${slideOriginalIndex}"]:not(.${swiper.params.slideDuplicateClass})`);
            swiper.lazy.loadInSlide(originalSlide.index(), false);
          } else {
            const duplicatedSlide = swiper.$wrapperEl.children(`.${swiper.params.slideDuplicateClass}[data-swiper-slide-index="${slideOriginalIndex}"]`);
            swiper.lazy.loadInSlide(duplicatedSlide.index(), false);
          }
        }
        swiper.emit('lazyImageReady', $slideEl[0], $imageEl[0]);
        if (swiper.params.autoHeight) {
          swiper.updateAutoHeight();
        }
      });

      swiper.emit('lazyImageLoad', $slideEl[0], $imageEl[0]);
    });
  },
  load() {
    const swiper = this;
    const {
      $wrapperEl, params: swiperParams, slides, activeIndex,
    } = swiper;
    const isVirtual = swiper.virtual && swiperParams.virtual.enabled;
    const params = swiperParams.lazy;

    let slidesPerView = swiperParams.slidesPerView;
    if (slidesPerView === 'auto') {
      slidesPerView = 0;
    }

    function slideExist(index) {
      if (isVirtual) {
        if ($wrapperEl.children(`.${swiperParams.slideClass}[data-swiper-slide-index="${index}"]`).length) {
          return true;
        }
      } else if (slides[index]) return true;
      return false;
    }

    function slideIndex(slideEl) {
      if (isVirtual) {
        return $(slideEl).attr('data-swiper-slide-index');
      }
      return $(slideEl).index();
    }

    if (!swiper.lazy.initialImageLoaded) swiper.lazy.initialImageLoaded = true;
    if (swiper.params.watchSlidesVisibility) {
      $wrapperEl.children(`.${swiperParams.slideVisibleClass}`).each((elIndex, slideEl) => {
        const index = isVirtual ? $(slideEl).attr('data-swiper-slide-index') : $(slideEl).index();
        swiper.lazy.loadInSlide(index);
      });
    } else if (slidesPerView > 1) {
      for (let i = activeIndex; i < activeIndex + slidesPerView; i += 1) {
        if (slideExist(i)) swiper.lazy.loadInSlide(i);
      }
    } else {
      swiper.lazy.loadInSlide(activeIndex);
    }
    if (params.loadPrevNext) {
      if (slidesPerView > 1 || (params.loadPrevNextAmount && params.loadPrevNextAmount > 1)) {
        const amount = params.loadPrevNextAmount;
        const spv = slidesPerView;
        const maxIndex = Math.min(activeIndex + spv + Math.max(amount, spv), slides.length);
        const minIndex = Math.max(activeIndex - Math.max(spv, amount), 0);
        // Next Slides
        for (let i = activeIndex + slidesPerView; i < maxIndex; i += 1) {
          if (slideExist(i)) swiper.lazy.loadInSlide(i);
        }
        // Prev Slides
        for (let i = minIndex; i < activeIndex; i += 1) {
          if (slideExist(i)) swiper.lazy.loadInSlide(i);
        }
      } else {
        const nextSlide = $wrapperEl.children(`.${swiperParams.slideNextClass}`);
        if (nextSlide.length > 0) swiper.lazy.loadInSlide(slideIndex(nextSlide));

        const prevSlide = $wrapperEl.children(`.${swiperParams.slidePrevClass}`);
        if (prevSlide.length > 0) swiper.lazy.loadInSlide(slideIndex(prevSlide));
      }
    }
  },
};

export default {
  name: 'lazy',
  params: {
    lazy: {
      enabled: false,
      loadPrevNext: false,
      loadPrevNextAmount: 1,
      loadOnTransitionStart: false,

      elementClass: 'swiper-lazy',
      loadingClass: 'swiper-lazy-loading',
      loadedClass: 'swiper-lazy-loaded',
      preloaderClass: 'swiper-lazy-preloader',
    },
  },
  create() {
    const swiper = this;
    Utils.extend(swiper, {
      lazy: {
        initialImageLoaded: false,
        load: Lazy.load.bind(swiper),
        loadInSlide: Lazy.loadInSlide.bind(swiper),
      },
    });
  },
  on: {
    beforeInit() {
      const swiper = this;
      if (swiper.params.lazy.enabled && swiper.params.preloadImages) {
        swiper.params.preloadImages = false;
      }
    },
    init() {
      const swiper = this;
      if (swiper.params.lazy.enabled && !swiper.params.loop && swiper.params.initialSlide === 0) {
        swiper.lazy.load();
      }
    },
    scroll() {
      const swiper = this;
      if (swiper.params.freeMode && !swiper.params.freeModeSticky) {
        swiper.lazy.load();
      }
    },
    resize() {
      const swiper = this;
      if (swiper.params.lazy.enabled) {
        swiper.lazy.load();
      }
    },
    scrollbarDragMove() {
      const swiper = this;
      if (swiper.params.lazy.enabled) {
        swiper.lazy.load();
      }
    },
    transitionStart() {
      const swiper = this;
      if (swiper.params.lazy.enabled) {
        if (swiper.params.lazy.loadOnTransitionStart || (!swiper.params.lazy.loadOnTransitionStart && !swiper.lazy.initialImageLoaded)) {
          swiper.lazy.load();
        }
      }
    },
    transitionEnd() {
      const swiper = this;
      if (swiper.params.lazy.enabled && !swiper.params.lazy.loadOnTransitionStart) {
        swiper.lazy.load();
      }
    },
    slideChange() {
      const swiper = this;
      if (swiper.params.lazy.enabled && swiper.params.cssMode) {
        swiper.lazy.load();
      }
    },
  },
};