jquery check if asp checkbox is checked
Assuming your checkbox is the only item on the page having the checkbox class:
var checked = $(".checkbox").is(':checked')
try...
if ($('#<%= checkboxRules.ClientID %>').is(':checked')) {
...
}
Since it is a server-side Checkbox, it will send something like <input type="checkbox" class="checkbox" />
as HTML to the client after ASP.NET processes the control.
The id of the checkbox isn't going to be checkboxRules as you have it in the source code. ASP.NET will make a concatenation of the server-side form id + master page id (if using a master page) + checkboxRules so in this case I won't use a selector that depends on element id.
We can make a jQuery selector as narrow as possible to only select inputs with a type of "checkbox" and with a CSS class of "checkbox".
$('input[type=checkbox] .checkbox').attr('checked')
will return the boolean value of the check status of the input. This will find any input on the page that is a checkbox with that CSS class.