Answers for "do something when checkbox is checked jquery"

jquery set checkbox checked

//jQuery 1.6+ use
$('.checkbox').prop('checked', true);
//jQuery 1.5.x and below use
$('.checkbox').attr('checked', true);

How to check whether a checkbox is checked in jQuery?

//using plane javascript 
if(document.getElementById('on_or_off_checkbox').checked) {
    //I am checked
} 

//using jQuery
if($('#on_or_off_checkbox').is(':checked')){
    //I am checked
}