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");      }