how can i check the checkbox is checked or not in jquery code example

Example 1: 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
}

Example 2: How do I check whether a checkbox is checked in jQuery?

$('#' + id).is(":checked")

Example 3: jquery if checkbox is checked

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