Enable and disable button using javascript and asp.net
<p>I am checking if user exists in database if exists I am showing message as "existed user" and then I need to disable the signup button if not I need to enable it.</p>

<p>I am unable to enable and disable the sign Up button.</p>

<p>Can anyone help me in this issue?</p>

<p>Here is my code:</p>

<pre><code> &lt;script type="text/javascript"&gt;
     $(function () {
         $("#&lt;% =btnavailable.ClientID %&gt;").click(function () {
             if ($("#&lt;% =txtUserName.ClientID %&gt;").val() == "") {
                 $("#&lt;% =txtUserName.ClientID %&gt;").removeClass().addClass('notavailablecss').text('Required field cannot be blank').fadeIn("slow");

             } else {
                 $("#&lt;% =txtUserName.ClientID %&gt;").removeClass().addClass('messagebox').text('Checking...').fadeIn("slow");
                 $.post("LoginHandler.ashx", { uname: $("#&lt;% =txtUserName.ClientID %&gt;").val() }, function (result) {
                     if (result == "1") {
                         $("#&lt;% =txtUserName.ClientID %&gt;").addClass('notavailablecss').fadeTo(900, 1);
                       document.getElementById(#&lt;% =btnSignUp.ClientID %&gt;').enabled = false;
                     }
                     else if (result == "0") {
                         $("#&lt;% =txtUserName.ClientID %&gt;").addClass('availablecss').fadeTo(900, 1);
                        document.getElementById('#&lt;% =btnSignUp.ClientID %&gt;').enabled = true;
                     }
                     else {
                         $("#&lt;% =txtUserName.ClientID %&gt;").addClass('notavailablecss').fadeTo(900, 1);
                     }
                 });
             }
         });

         $("#&lt;% =btnavailable.ClientID %&gt;").ajaxError(function (event, request, settings, error) {
             alert("Error requesting page " + settings.url + " Error:" + error);
         });
     });
&lt;/script&gt;
</code></pre>
