how to check checkbox 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: jquery check if checkbox is not checked

if (!$("#checkboxID").is(":checked")) {
    // do something if the checkbox is NOT checked
}

Example 3: check whether a checkbox is checked in jQuery

if ($('#grepperRocks').is(':checked')) {
	// this checkbox is checked
}

Example 4: jquery see if checkbox is checked

$('input.checkbox').is(':checked')