checkbox jquery checked

1//jQuery 1.6+ use
2$('.checkbox').prop('checked', true);
3//jQuery 1.5.x and below use
4$('.checkbox').attr('checked', true);

1//using plane javascript 
2if(document.getElementById('on_or_off_checkbox').checked) {
3    //I am checked
4} 
5
6//using jQuery
7if($('#on_or_off_checkbox').is(':checked')){
8    //I am checked
9}

1$( "SELECTOR" ).attr( "checked" )  // Returns ‘true’ if present on the element, returns undefined if not present
2$( "SELECTOR" ).prop( "checked" ) // Returns true if checked, false if unchecked.
3$( "SELECTOR" ).is( ":checked" ) // Returns true if checked, false if unchecked.

1//jQuery 1.6+ use:
2$('.checkboxClass').prop('checked', true);
3//jQuery 1.5.x and below use:
4$('.checkboxClass').attr('checked', true);

1if ($('#check_id').is(":checked"))
2{
3  // it is checked
4}

1var isExpanded = $(this).attr('checked') == "checked";
2