【延迟加载】

ImagesLazyLoad 图片延迟加载效果
http://www.cnblogs.com/cloudgamer/archive/2010/03/03/ImagesLazyLoad.html
Lazyload 延迟加载效果
http://www.cnblogs.com/cloudgamer/archive/2010/02/01/LazyLoad.html

非首屏内容的延迟加载

function loadSecondaryScreen(elem, callback) {
    var $window =  $(window);
    var elemTop = elem.offset().top;
    var viewportH = $window.height();
    var loaded = 0;
    if (elemTop > viewportH) {
        $window.bind('scroll', function() {
            if (loaded == 0) {
                loaded = 1;
                $window.unbind('scroll');
                callback();
            }
        });
    } else {
        callback();
    }
}