jQuery if checkbox is checked

if ($('input.checkbox_check').is(':checked')) {

for jQuery 1.6 or higher:

if ($('input.checkbox_check').prop('checked')) {
    //blah blah
}

the cross-browser-compatible way to determine if a checkbox is checked is to use the property https://api.jquery.com/prop/

this $('#checkboxId').is(':checked') for verify if is checked

& this $("#checkboxId").prop('checked', true) to check

& this $("#checkboxId").prop('checked', false) to uncheck

If none of the above solutions work for any reason, like my case, try this:

  <script type="text/javascript">
    $(function()
    {
      $('[name="my_checkbox"]').change(function()
      {
        if ($(this).is(':checked')) {
           // Do something...
           alert('You can rock now...');
        };
      });
    });
  </script>

If checked:

$( "SELECTOR" ).attr( "checked" )  // Returns ‘true’ if present on the element, returns undefined if not present
$( "SELECTOR" ).prop( "checked" ) // Returns true if checked, false if unchecked.
$( "SELECTOR" ).is( ":checked" ) // Returns true if checked, false if unchecked.

Get the checked val:

$( "SELECTOR:checked" ).val()

Get the checked val numbers:

$( "SELECTOR:checked" ).length

Check or uncheck checkbox

$( "SELECTOR" ).prop( "disabled", false );
$( "SELECTOR" ).prop( "checked", true );