jquery checkbox checked

//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
}

$( "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.

if ($('#check_id').is(":checked"))
{
  // it is checked
}

$(your_checkbox).is(':checked');

$("checkbox").is(":checked")

// Check a checkbox
$(selector).prop('checked', true);
// Un-check a checkbox
$(selector).prop('checked', false);
// Determine if checked or not
isChecked = $(selector).prop('checked');

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

var isExpanded = $(this).attr('checked') == "checked";

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