Fixed navigation effects implemented by jquery

1.jquery code , .nav For navigation class
$(function(){ 
  $(window).scroll(function() {
 if($(window).scrollTop()>=250){
  $(".nav").addClass("fixedNav");
 }else{
  $(".nav").removeClass("fixedNav");
 }
  });
});
2.CSS code
.fixedNav{
 position:fixed;
 top:0px;
 left:0px;
 width:100%;
 z-index:100000;
 _position:absolute;
 _top:expression(eval(document.documentElement.scrollTop));
}
3.HTML code
<div class="nav">
    <p> Navigation fixed </p>
</div>