js实现弹窗居中的简单实例

.windowBox{

  width:500px;

}

.mid-tanBox{

  position: fixed; top: 50%; left: 50%;  margin-left: -250px; background: #fff; border:1px solid red; display:none

}

<div class='windowBox'>

 <div class ="mid-tanBox"></div>

 <div class="jclick">弹窗</div>

</div>

$(".jclick").click(function(i){

 var height = $(".mid-tanBox").height();

 var eheight = height/2;

 $(".mid-tanBox").eq(i).css("margin-top","-eheight");

})