Passing value from code-behind to Javascript

Question

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;
 $("#progressbar").progressbar({
 value: pct
 });
 });
 </script>
 </asp:Content>
 <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
 ...
 <input type="hidden" runat="server" id="filesPercentage" /> 
 <div id="progressbar"></div> 
 ...
 </asp:Content>

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.

• Adam Roderick: Does the hidden field contain the value if you view the source?
• O.O: filesPercentage is likely not going to be id of the control once it is rendered.

Answer 1

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

Answer 2

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)

http://jsfiddle.net/pxfunc/QyZSs/

• Laplace: Good job on solving my first problem and anticipating the next problem I would have run into. This worked perfectly.

Answer 3

Try this

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

Answer 4

.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();

Answer 5

This is a bit cleaner IMHO :-)

$("#progressbar").progressbar({
 value: $("#<%=filesPercentage.ClientID%>").val()
});