Passing value from code-behind to Javascript

I am using a jQueryUI ProgressBar to show users how much allowed file storage they have used. The percentage is calculated in code-behind and should be passed to Javascript.

Aspx Code

    <asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
        <script type="text/javascript">
            $(function () {
                var pct = document.getElementById("filesPercentage").value;
                    value: pct

    <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
     <input type="hidden" runat="server" id="filesPercentage" />                      
     <div id="progressbar"></div>         

Code Behind

protected void Page_Load(object sender, EventArgs e)
   filesPercentage.Value = "85";

It seems like it can't get the percentage number from the hidden field. Any help would be appreciated.



since your hidden field is a server control it could be that the ID is getting generated to something other than filesPercentage (probably something like ctl00_ctl00_filesPercentage)

  • You may need to apply the generated client ID to your javascript document.getElementById("<%=filesPercentage.ClientID%>").value;
  • Or use another way of selecting the hidden value, such as $('[hidden's parent element] input[type="hidden"]').val()

additionally, it looks like progressbar value is expecting a number, so you may need to do value: pct * 1 or value: parseInt(pct)


You need to get the rendered id of your hidden input

var pct = document.getElementById("<%=filesPercentage.ClientID%>").value;

and from the moment that you run the input on server its better to use the asp:HiddenField and not the input


Try this

var pct = document.getElementById("<%=filesPercentage.ClientID %>").value;

.net will modify the id you give a control to ensure it is unique, so you are not accessing it with the correct id. If you give the hidden field a unique class name, you can access the value that way:

<input type="hidden" runat="server" id="filesPercentage" class="hiddenClass" /> 
var pct = $('.hiddenClass').val();

This is a bit cleaner IMHO :-)

  value: $("#<%=filesPercentage.ClientID%>").val()


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