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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              <h1>Lazy loading images</h1>
<p>Main purpose of lazy loading: save <strong>your</strong> bandwidth. Side effect: user's initial page load time might reduce. However user may also see images flashing as they are loaded.</p>
<h2>Challenges:</h2>
<dl>
  <dt>Should work JavaScript disabled</dt>
  <dd>Just without lazy loading of course. Also means Google and other search engines can access the image.</dd>
  <dt>Should have short syntax</dt>
  <dd>Many solutions I've seen seem to easily become quite verbose with their HMTL. Especially if you want to support the above.</dd>
  <dt>Should work nicely in mobile</dt>
  <dd>I don't want my iPad to load them with extra 2 seconds delay when on 4G!</dd>
  <dt>Don't be slow!</dt>
  <dd>Some solutions seem to be very slow on initial page load: in my tests with mere 50 images jQuery JAIL plugin spent 150 ms setting stuff up!<br /><small>Yes, that is a lot. It would double the page JS init time on my production site.</small></dd>
  <dt>Should account for both vertical and horizontal scrolling.</dt>
  <dd>Some solutions only account for vertical scrolling.</dd>
  <dt>Should work on Internet Explorer 8+</dt>
  <dd>The smaller you make it and the more feature requirements you add the more likely you are going to run into compability barriers.</dd>
</dl>

<noscript data-lazy-img><img alt="Test" title="FYI: This does not work on IE8 and below" src="http://i1-news.softpedia-static.com/images/news2/Critical-Out-of-Band-Patch-for-Internet-Explorer-8-2.jpg" height="417" width="417" /></noscript>

<!--[if IE 9]><!--><noscript data-lazy-img><!--<![endif]--><img alt="Test" src="http://placehold.it/183x360" height="360" width="183" /><!--[if IE 9]><!--></noscript><!--<![endif]-->

<!--[if IE 9]><!--><noscript data-lazy-img><!--<![endif]--><img alt="Test" src="http://placehold.it/267x300" height="300" width="267" /><!--[if IE 9]>--></noscript><!--<![endif]-->

<!--[if IE 9]><!--><noscript data-lazy-img><!--<![endif]--><img alt="Test" src="http://placehold.it/193x156" height="156" width="193" /><!--[if IE 9]>--></noscript><!--<![endif]-->

Image that fails to load:
<!--[if IE 9]><!--><noscript data-lazy-img><!--<![endif]--><img class="fails" alt="Test" src="#obviously-is-not-an-image" height="300" width="300" /><!--[if IE 9]>--></noscript><!--<![endif]-->

<h2>The Requirements</h2>
<ul>
  <li>Add before image: <code>&lt;!--[if IE 9]&gt;&lt;!--&gt;&lt;noscript data-lazy-img&gt;&lt;!--&lt;![endif]--&gt;</code></li>
  <li>Add after image: <code>&lt;!--[if IE 9]&gt;&lt;!--&gt;&lt;/noscript&gt;&lt;!--&lt;![endif]--&gt;</code></li>
  <li>Image must have width and height attributes set (as always with lazy loading).</li>
  <li>And that is all that is into it in HTML. Rest is JavaScript.</li>
</ul>

<h2>The Good</h2>
<p>Shortest syntax I know of that also supports JS disabled.</p>
<p>Answers all the challenges in a positive manner.</p>

<h2>The Bad</h2>
<p>There can be a small delay after page is first rendered and JavaScript execution which means page layout might be re-calculated when noscript elements are replaced with images.</p>
<p>Also doesn't support responsive loading if you fancy that.</p>

<h2>The Weird &amp; Ugly</h2>
<p>Internet Explorer Conditional Comments: IE 8 and below don't allow accessing contents of noscript elements.</p>
<p>With some simple conditional comments we can hide noscript element tags from those IEs so they work as if JS is disabled.</p>
<p>But then we get no lazy loading.</p>

            
          
!
            
              /* just to add distance between images */
img {
  border: 1px dotted #ccc;
  display: block;
  margin: 20em 10em;
}

img.fails {
  border-color: red;
  margin-top: 0;
}

/* a little bit of style */
html {
  padding: 2em;
}

dl {
  margin: 1em;
}

dt {
  display: list-item;
  font-weight: bold;
}

dd {
  font-size: smaller;
  margin: 1em;
}
            
          
!
            
              $(function() {
  var $window = $(window),
      images = [],
      imagesToBeLoaded = 0,
      i,
      src;

  function throttle(func, wait) {
    var timeout;
    return function() {
      var context = this, args = arguments;
      if(!timeout) {
        timeout = setTimeout(function() {
          timeout = null;
        }, wait);
        func.apply(context, args);
      }
    };
  }
  
  function inViewport($el) {
    var top = $window.scrollTop(),
        left = $window.scrollLeft(),
        bottom = top + $window.height(),
        right = left + $window.width(),
        offset = $el.offset(),
        thisTop = offset.top,
        thisLeft = offset.left,
        thisBottom = thisTop + $el.outerHeight(),
        thisRight = thisLeft + $el.outerWidth();

    return !(
      bottom < thisTop ||
      top > thisBottom ||
      right < thisLeft ||
      left > thisRight
    );
  }

  // throttle so we don't do too many calls
  var lazyScroll = throttle(function() {
    // have all images been loaded?
    if(imagesToBeLoaded > 0) {
      for(i = 0; i < images.length; i++) {
        // data is there if nothing has been done to it
        src = images[i].data('src');
        // see if the image is in the view
        if(src && inViewport(images[i])) {
          // create a nice closure here
          (function(img, src, i, $img) {
            img.onload = function() {
              console.log('Loaded ' + i + ' ' + img.src);
              $img.attr('src', img.src);
              imagesToBeLoaded--;
            };
            img.onerror = function() {
              console.log('Could not load ' + i + ' ' + img.src);
              imagesToBeLoaded--;
            };
            // important to remove this to avoid duplicate calls
            $img.removeData('src');
            // start loading the image
            img.src = src;
          })(new Image(), src, i, images[i]);
        }
      }
    } else {
      // cleanup
      images = void 0;
      // why keep listening if there is nothing to listen
      $window.off('resize scroll touchmove', lazyScroll);
      // all images are loaded
      console.log('Unloaded event listener');
    }
  }, 50);
  
  $('noscript[data-lazy-img]').each(function() {
    var $this = $(this),
        $img = $(this.innerText || $this.text()).filter('img');
    // make sure we got something
    if($img.length === 1) {
      // remember the real image
      $img.data('src', $img.attr('src'));
      // use a blank image
      $img.attr('src', 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7');
      // cache a reference
      images.push($img);
      // replace noscript element with the image
      $this.replaceWith($img);
      imagesToBeLoaded++;
    }
  });
  // only add if we need it
  if(imagesToBeLoaded) {
    lazyScroll();
    $window.on('resize scroll touchmove', lazyScroll);
  }
});
            
          
!
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