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 if checkbox 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.

Example 3: How do I check whether a checkbox is checked in jQuery?

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