/// <reference path="../typings/zepto/zepto.d.ts" />

(function ($) {
    $.fn.lazyload = function (ops) {
        var $w = $(this);
        var options = <lazyloadOptions>$.extend({filter: "*[data-lazy]", preloadHeight: 50 }, ops);
        var height =$w.height();
        $w.on("scroll", e => {
            var elements = $(options.filter + "[data-origin]");
            var top_end = (<HTMLElement>$w[0]).scrollTop +height+ options.preloadHeight;
            elements.each((index:number, item: HTMLElement) => {
                var $item: ZeptoCollection = $(item);
                var t = Math.floor($item.offset().top);
                if (t <= top_end) {
                    var origin = $item.attr("data-origin");
                    $item.removeAttr("data-origin").removeAttr("data-lazy");
                    switch (item.tagName.toLowerCase()) {
                        case "img":
                            $item.attr({ src: origin, a: origin });
                            break;
                        default:
                            $item.load(origin);
                            break;
                    }
                }
                return true;
            });
        });
        $w.trigger("scroll");
    };
})(Zepto);

interface lazyloadOptions {
    filter: string;//过滤器
    preloadHeight: number;//预加载高度
}

<script type="text/javascript">
        $(function () {
            $(".page").lazyload();
        });
    </script>