JQuery计算当前Dom结构在浏览器窗口中被显示方法（懒加载原理）

var dealImg = $("[nmshow]");
    var dealLength = dealImg.length;
    var arrayguard = new Array();//记录已被筛选的dealImg对象
    
    function dealImgIsShow(){    //单子显示出来计算一次pv
        var tempscrollTop = $(document).scrollTop();
        var windowHeight = $(window).height();
        for(var i=0;i<dealLength;i++){
            if(!arrayguard[i]){
                if(windowHeight + tempscrollTop > dealImg.eq(i).offset().top+dealImg.eq(i).height()){
                    arrayguard[i] = 1;//当前对象已经被标记
                    eval(dealImg.eq(i).attr("nmshow"));
                }    
            }
        }
    }
    if (dealLength > 0) {
        dealImgIsShow();
        $(window).scroll(function(){//监听属性是nmshow的img标签是否被展示
            dealImgIsShow();
        });
    }