一段实现页面上的图片延时加载的js - 架构师-解占辉- 51CTO技术博客企业库|免费b2b网站

代码

lazyLoad=(function() {
    var map_element = {};
    var element_obj = [];
    var download_count = 0;
    var last_offset = -1;
    var doc_body;
    var doc_element;
    var lazy_load_tag;
    function initVar(tags) {
        doc_body = document.body;
        doc_element = document.compatMode == 'BackCompat' ? doc_body: document.documentElement;
        lazy_load_tag = tags || ["img", "iframe"];
    };
    function initElementMap() {
        var all_element = [];
        //从所有相关元素中找出需要延时加载的元素
        for (var i = 0,
        len = lazy_load_tag.length; i < len; i++) {
            var el = document.getElementsByTagName(lazy_load_tag[i]);
            for (var j = 0,
            len2 = el.length; j < len2; j++) {
                if (typeof(el[j]) == "object" && el[j].getAttribute("lazy_src")) {
                    element_obj.push(all_element[key]);
                }
            }
        }

        for (var i = 0,
        len = element_obj.length; i < len; i++) {
            var o_img = element_obj[i];
            var t_index = getAbsoluteTop(o_img);//得到图片相对document的距上距离
            if (map_element[t_index]) {
                map_element[t_index].push(i);
            } else {
                //按距上距离保存一个队列
                var t_array = [];
                t_array[0] = i;
                map_element[t_index] = t_array;
                download_count++;//需要延时加载的图片数量
            }
        }

    };
    function initDownloadListen() {
        if (!download_count) return;
        var offset = (window.MessageEvent && !document.getBoxObjectFor) ? doc_body.scrollTop: doc_element.scrollTop;
        //可视化区域的offtset=document的高+
        var visio_offset = offset + doc_element.clientHeight;
        if (last_offset == visio_offset) {
            setTimeout(initDownloadListen, 200);
            return;
        }
        last_offset = visio_offset;
        var visio_height = doc_element.clientHeight;
        var img_show_height = visio_height + offset;
        for (var key in map_element) {
            if (img_show_height > key) {
                var t_o = map_element[key];
                var img_vl = t_o.length;
                for (var l = 0; l < img_vl; l++) {
                    element_obj[t_o[l]].src = element_obj[t_o[l]].getAttribute("lazy_src");
                }
                delete map_element[key];
                download_count--;
            }
        }
        setTimeout(initDownloadListen, 200);
    };
    function getAbsoluteTop(element) {
        if (arguments.length != 1 || element == null) {
            return null;
        }
        var offsetTop = element.offsetTop;
        while (element = element.offsetParent) {
            offsetTop += element.offsetTop;
        }
        return offsetTop;
    }
    function init(tags) {
        initVar(tags);
        initElementMap();
        initDownloadListen();
    };
    return {
        init: init
    }
})();

chlid.find("img[init_src]").each(function(){
                    $(this).attr("src",$(this).attr("init_src"));
                    $(this).removeAttr("init_src");

                });