Function lazyload

src/utils/general.ts:763–823

(doc, scrollElement = '.mdl-layout__content')

let lazyimages: any[] = [];

export function lazyload(doc, scrollElement = '.mdl-layout__content') {
  /* lazyload.js (c) Lorenzo Giuliani
   * MIT License (http://www.opensource.org/licenses/mit-license.html)
   *
   * expects a list of:
   * `<img src="blank.gif" data-src="my_image.png" width="600" height="400" class="lazy">`
   */
  // eslint-disable-next-line
  function loadImage(el, fn) {
    if (!j.$(el).is(':visible')) return false;
    if (j.$(el).hasClass('lazyBack')) {
      j.$(el)
        .css('background-image', `url(${el.getAttribute('data-src')})`)
        .removeClass('lazyBack');
    } else {
      const img = new Image();
      const src = el.getAttribute('data-src');
      img.onload = function () {
        if (el.parent) el.parent.replaceChild(img, el);
        else el.src = src;
        // eslint-disable-next-line
        fn ? fn() : null;
      };
      img.src = src;
    }
  }

  for (let i = 0; i < lazyimages.length; i++) {
    $(lazyimages[i]).addClass('init');
  }

  lazyimages = [];
  const query = doc.find('img.lazy.init, .lazyBack.init');
  const processScroll = function () {
    for (let i = 0; i < lazyimages.length; i++) {
      if (utils.elementInViewport(lazyimages[i], 600)) {
        // eslint-disable-next-line
        loadImage(lazyimages[i], function() {
          lazyimages.splice(i, i);
        });
      }
      if (!$(lazyimages[i]).length) {
        lazyimages.splice(i, i);
      }
    }
  };
  // Array.prototype.slice.call is not callable under our lovely IE8
  for (let i = 0; i < query.length; i++) {
    lazyimages.push(query[i]);
    $(query[i]).removeClass('init');
  }

  processScroll();

  if (!lazyloaded) {
    lazyloaded = true;
    doc.find(scrollElement).scroll(function () {
      processScroll();