jquery计算出left和top,让一个div水平垂直居中的简单实例

if($("#cont1").css("position")!="fixed"){
        $("#cont1").css("position","absolute");
        var dw = $(window).width();
        var ow = $("#cont1").outerWidth();
        var dh = $(window).height();
        var oh = $("#cont1").outerHeight();
        var l = (dw - ow) / 2;
        var t = (dh - oh) / 2 > 0 ? (dh - oh) / 2 : 10;
        var lDiff = $("#cont1").offset().left - $("#cont1").position().left;
        var tDiff = $("#cont1").offset().top - $("#cont1").position().top;
        l = l + $(window).scrollLeft() - lDiff;
        t = t + $(window).scrollTop() - tDiff;
        $("#cont1").css("left",l + "px");
        $("#cont1").css("top",t + "px");
      }