Question

Am trying to sortout this small issue from past hour :

<script type="text/javascript">
$(document).ready(function(){        
    $("input[name='isClubMember']:checkbox").mousedown(function() {
         if (!$(this).is(':checked')) {
            this.checked = confirm("Are you sure?");
            $(this).trigger("change");
         }
    });
 });
</script>

Funnily this works in JSFiddle ..but not in my jsp page.
Sample

The above code gives me null error at this line (in Debug console)

 $("input[name='isClubMember']:checkbox").mousedown(function() {

JQ -Ver : 1.7.2 Browser : IE8

Update :
Error in IE console :

 'null' is null or not an object 

at the above mentioned line

Answer 1

It looks like your JSP page includes the Prototype library after jQuery.

Prototype’s $() function takes an id and returns null if it cannot find the element, which is consistent with the behavior you’re observing.

Try using jQuery instead of $ everywhere in your code:

jQuery("input[name='isClubMember']:checkbox").mousedown(function() {
    // ...
});

Or put your code in a closure that is passed the jQuery object in a $ argument:

(function($) {
    // The rest of your code...
})(jQuery);

Or take advantage of the fact that a ready handler is passed the same $ argument:

jQuery(document).ready(function($) {
    // The code in your 'ready' handler...
});

You may also want to run jQuery in noConflict mode, to avoid overriding Prototype’s $() function if the order of inclusion changes.