Accessing asp:HiddenField in Javascript

Question

I am very confused when it comes to using asp:hiddenfields .

Here is my code:

<asp:HiddenField ID ="CurrentAnswer" runat="server" Value="-1" />

and in a js file loaded in that html page:

$(document).ready(function () {
    alert(document.getElementById("<%= CurrentAnswer.ClientID %>"));
});

This value returns null. It will work if i put it into the same asp webform, but not in a separate js file.I have seen this done on just about every page I looked at. here for example. I have no idea why this is not working. Any thoughts?

Answer 1

If you want to keep the javascript in sepearate js file, you want to use Static (or Predictable) for ID.

<asp:HiddenField ID="CurrentAnswer" runat="server" Value="-1" 
   ClientIDMode="Static" />

Separate JavaScript File

$(document).ready(function () {
    alert($("#CurrentAnswer").val());
});

Answer 2

If the CurrentAnswer ID is not dynamic, you can do this:

$(document).ready(function () {
    alert(document.getElementById("CurrentAnswer"));
});

Of course, this will give you an object, so you can call .val() to get the value of it.