Web优化 页面性能优化 自定义函数延迟触发 jquery插件

今天碰到一个很奇快的需求，大致如下：html页面有很多div容器，每个div容器的数据都是通过ajax请求来处理的。一般情况处理ajax请 都在windows的load事件中，由于页面的div容器太多造成windows的load事件中ajax请求太多；所以我们只需要处理那些在浏览器中 看得见的div容器。假如我们现在有10个div容器，每个屏幕刚好显示1个div容器，如果我们放到windows的load事件中，那么刚开始就有 10个ajax请求。其实用户可能根本不会看到后面几个div容器，所以我们通过这个插件来延迟这些ajax的请求，刚加载页面有1个或2个ajax请求，当滚动条滚到相应div的时候，div再发起ajax请求。

jquery.lazyevent.js插件源代码:

(function ($, window) {
    var $window = $(window);

    $.fn.lazyevent = function (options) {
        var elements = this;
        var settings = {
            threshold: 0,
            event: "scroll",
            container: window,
            skip_invisible: true,
            fn: null,
            data: null
        };
        function update() {
            var counter = 0;

            elements.each(function () {
                var $this = $(this);
                if (settings.skip_invisible && !$this.is(":visible")) {
                    return;
                }
                /*               if (!belowthefold(this, settings) && !rightoffold(this, settings)) {
                $this.trigger("fire");
                }*/
                if (inviewport(this, settings)) {
                    $this.trigger("fire");
                }
            });

        }
        if (options) {
            $.extend(settings, options);
        }
        var $container = (settings.container === undefined || settings.container === window) ? $window : $(settings.container);

        if (0 === settings.event.indexOf("scroll")) {
            $container.bind(settings.event, function (event) { return update(); });
        }
        this.each(function () {
            var self = this;
            var $self = $(self);
            self.fired = false;
            $self.one("fire", function () {
                if (!this.fired) {
                    if (settings.fn) {
                        settings.fn.call(self, settings.data);
                    }
                    self.fired = true;
                    var temp = $.grep(elements, function (element) { return !element.fired; });
                    elements = $(temp);
                }
            });

            if (0 !== settings.event.indexOf("scroll")) {
                $self.bind(settings.event, function (event) {
                    if (!self.fired) {
                        $self.trigger("fire");
                    }
                });
            }
        });

        $window.bind("resize", function (event) {
            update();
        });


        var belowthefold = function (element, settings) {
            var fold;

            if (settings.container === undefined || settings.container === window) {
                fold = $window.height() + $window.scrollTop();
            } else {
                fold = $container.offset().top + $container.height();
            }
            return fold <= $(element).offset().top - settings.threshold;
        };

        var rightoffold = function (element, settings) {
            var fold;

            if (settings.container === undefined || settings.container === window) {
                fold = $window.width() + $window.scrollLeft();
            } else {
                fold = $container.offset().left + $container.width();
            }

            return fold <= $(element).offset().left - settings.threshold;
        };
        var abovethetop = function (element, settings) {
            var fold;

            if (settings.container === undefined || settings.container === window) {
                fold = $window.scrollTop();
            } else {
                fold = $container.offset().top;
            }

            return fold >= $(element).offset().top + settings.threshold + $(element).height();
        };

        var leftofbegin = function (element, settings) {
            var fold;

            if (settings.container === undefined || settings.container === window) {
                fold = $window.scrollLeft();
            } else {
                fold = $container.offset().left;
            }

            return fold >= $(element).offset().left + settings.threshold + $(element).width();
        };
        var inviewport = function (element, settings) {
            return !abovethetop(element, settings) && !leftofbegin(element, settings) &&
        !belowthefold(element, settings) && !rightoffold(element, settings);

        };
        update();
        return this;
    };

})(jQuery, window);

jquery.lazyevent..min.js代码：

(function(a,c){var b=a(c);a.fn.lazyevent=function(j){var g=this;var l={threshold:0,event:"scroll",container:c,skip_invisible:true,fn:null,data:null};function m(){var n=0;g.each(function(){var o=a(this);if(l.skip_invisible&&!o.is(":visible")){return}if(h(this,l)){o.trigger("fire")}})}if(j){a.extend(l,j)}var d=(l.container===undefined||l.container===c)?b:a(l.container);if(0===l.event.indexOf("scroll")){d.bind(l.event,function(n){return m()})}this.each(function(){var o=this;var n=a(o);o.fired=false;n.one("fire",function(){if(!this.fired){if(l.fn){l.fn.call(o,l.data)}o.fired=true;var p=a.grep(g,function(q){return !q.fired});g=a(p)}});if(0!==l.event.indexOf("scroll")){n.bind(l.event,function(p){if(!o.fired){n.trigger("fire")}})}});b.bind("resize",function(n){m()});var f=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.height()+b.scrollTop()}else{o=d.offset().top+d.height()}return o<=a(n).offset().top-p.threshold};var k=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.width()+b.scrollLeft()}else{o=d.offset().left+d.width()}return o<=a(n).offset().left-p.threshold};var e=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.scrollTop()}else{o=d.offset().top}return o>=a(n).offset().top+p.threshold+a(n).height()};var i=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.scrollLeft()}else{o=d.offset().left}return o>=a(n).offset().left+p.threshold+a(n).width()};var h=function(n,o){return !e(n,o)&&!i(n,o)&&!f(n,o)&&!k(n,o)};m();return this}})(jQuery,window);

html调用代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>lazyevent</title>
    <script type="text/javascript" src="Scripts/jquery-1.7.js"></script>
    <script type="text/javascript" src="Scripts/jquery.lazyevent.js"></script>
    <style type="text/css">
        /*      .test
        {
            height: 500px;
            display: inline-block;
             4000px;
        }
        .test div
        {
            float: left;
        }
      */.test div
        {
            width: 500px;
            height: 500px;
        }
    </style>
</head>
<body>
    <div style="height: 200px">
    </div>
    <div class="test">
        <div style="background-color: Green">
            Green</div>
        <div style="background-color: Lime">
            Lime</div>
        <div style="background-color: Maroon; display:none">
            Maroon</div>
        <div style="background-color: Olive">
            Olive</div>
        <div style="background-color: Red; display: none">
            Red</div>
        <div style="background-color: ButtonFace">
            ButtonFace</div>
        <div style="background-color: Aqua">
            Aqua</div>
        <div style="background-color: AppWorkspace">
            AppWorkspace</div>
    </div>
    <script type="text/javascript">
        $(function () {
            $(".test div").lazyevent({
                data: "hello word",
                fn: function (data) {
                    var html = $(this).html();
                    alert(data + ":" + html);
                }
            });
        });
    </script>
</body>
</html>