control revisit page

the popup window will be prompted when loading the page, and then user click the Close button on popup window to close.
now i would like to control the popup window only prompted when user first time visit. for the re-visit, it will not prompt.

but now it is failed to control when the user revisit the page, it still prompt in the below coding.
how can i hide the popup window when user revisit? 
 
 
 
 
 <script type="text/javascript">
 
 
  
          $(document).ready(function() {
     
     
     if(document.getElementById("visitCount").value !="1"){
       $('#Dialog').show();
       }
     //setTimeout($.TAF.ui.hideLoadingOverlay, 3000);
    });
 
     function ClickClose(){
 $("#Dialog").hide();
 document.getElementById("visitCount").value="1";
 var hiddenFiled=document.getElementById("visitCount").value;
 alert(hiddenField);
 
}

</script>
 
 <style>
 .modal {
            display: none;
            position: fixed;
            z-index: 999;
            padding-top: 100px;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            overflow: auto;
            background-color: rgb(0,0,0);
            background-color: rgba(0,0,0,0.4);
        }
</style>   

<!--testing begin-->
    <input type="hidden" id="visitCount" name="visitCount" />
<div id="Dialog" class="modal" tabindex="-1" >
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-header">
<h2 class="modal-title">  Testing</h2></div>
<div class="modal-body">
<div id="infoDetail"><p>
  <p>Content</p>
 
</div>
</div>
<div class="modal-footer"><div class="btn-center">
<button id="Close" onClick="ClickClose();"  value="Close"/>
</div>
</div>
</div>
</div>
</div>
  <!--testing end-->