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();
});
}