Unable to get a Hidden element in ASP.NET 4 from Javascript

I need help to find a hidden button in Javascript. I a开发者_如何学Gom using ASP.NET 4.

I can find a "visible = True" but when i try to find a hidden element it says object not found

    <script type="text/javascript">
    function ShowAge() 
     {
    var elem = document.getElementById('MainContent_chbFilter');
        if (elem != null)
            alert("Found 1");
        else
            alert("Not Found 1");
    var elemc = document.getElementById('MainContent_txtMSISDN');
        if (elemc != null)
            alert("Found 4");
        else
            alert("Not Found 4");
    }
   </script>

I am using asp:content Please help

In ASP.NET when you hide an element it is not rendered in the HTML at all. This is in contrast to using the hidden property in CSS, where the element is still there, just visually hidden. If you want to "hide" it server-side, but still make it available in the DOM, you should add style="display:none;" in your ASPX.

If an element has been hidden serverside (I'm assuming this is what you've done), this means that it won't get rendered onto the page, which is why Javascript won't find it in the DOM.

What you want is to assign it a CSS class (.hidden, for example) with display:none. You can then revert it back to display:block through Javascript.

If you're setting Visible=False to an element in the server-side code than it won't render to the page, so the JavaScript won't be able to access it.