Lazyload JS

README.md

#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">

example.html

<img src="blank.gif" class="lazy" data-src="/images/full-size.jpg" width="240" height="152">

jquery.lazyload.js

!function(window){
    
    function loadImage($el, $fn) {
        jQuery($el).attr('src', jQuery($el).attr('data-src'));
        $fn ? $fn() : null;
    }
    
    function elementInViewport($el) {
        var $rect = $el.getBoundingClientRect();
        return ($rect.top >= 0 && $rect.left >= 0 && $rect.top <= (window.innerHeight || document.documentElement.clientHeight)
        );
    }
    
    jQuery(document).ready(function() {
        
        var images = [],
        query = jQuery('img.lazy'),
        processScroll = function() {
            jQuery.each(images, function(i, img) {
                if (elementInViewport(img)) {
                    loadImage(img, function () {
                        images.splice(i, 1);
                    });
                }
            });
        };
        
        query.each(function() {
           images.push(this);
        });
        
        processScroll();
        jQuery(window).bind('scroll', processScroll);
        
    });
    
}(this);

lazyload.js

!function(window){
  var $q = function(q, res){
        if (document.querySelectorAll) {
          res = document.querySelectorAll(q);
        } else {
          var d=document
            , a=d.styleSheets[0] || d.createStyleSheet();
          a.addRule(q,'f:b');
          for(var l=d.all,b=0,c=[],f=l.length;b<f;b++)
            l[b].currentStyle.f && c.push(l[b]);

          a.removeRule(0);
          res = c;
        }
        return res;
      }
    , addEventListener = function(evt, fn){
        window.addEventListener
          ? this.addEventListener(evt, fn, false)
          : (window.attachEvent)
            ? this.attachEvent('on' + evt, fn)
            : this['on' + evt] = fn;
      }
    , _has = function(obj, key) {
        return Object.prototype.hasOwnProperty.call(obj, key);
      }
    ;

  function loadImage (el, fn) {
    var img = new Image()
      , src = el.getAttribute('data-src');
    img.onload = function() {
      if (!! el.parent)
        el.parent.replaceChild(img, el)
      else
        el.src = src;

      fn? fn() : null;
    }
    img.src = src;
  }

  function elementInViewport(el) {
    var rect = el.getBoundingClientRect()

    return (
       rect.top    >= 0
    && rect.left   >= 0
    && rect.top <= (window.innerHeight || document.documentElement.clientHeight)
    )
  }

    var images = new Array()
      , query = $q('img.lazy')
      , processScroll = function(){
          for (var i = 0; i < images.length; i++) {
            if (elementInViewport(images[i])) {
              loadImage(images[i], function () {
                images.splice(i, i);
              });
            }
          };
        }
      ;
    // Array.prototype.slice.call is not callable under our lovely IE8 
    for (var i = 0; i < query.length; i++) {
      images.push(query[i]);
    };

    processScroll();
    addEventListener('scroll',processScroll);

}(this);​