how to know checkbox is checked in jquery

how to know checkbox is checked in javascript, Here we are provide a example similar to that 
 
function selectcheckbox(x){var cls = $(x).attr(‘class’);if($(‘.’+cls).attr(‘checked’)){alert(‘chek box is checked’);}else { alert(‘check box is unchecked’);}}
Select Check box
code for this example :

function selectcheckbox(x){
var cls = $(x).attr(‘class’);

if($(‘.’+cls).attr(‘checked’)){
alert(‘chek box is checked’);
}
else { alert(‘check box is unchecked’);}

}

Select Check box