jquery checkbox

1$('.myCheckbox').prop('checked', true);
2$('.myCheckbox').prop('checked', false);

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);

1$(document).ready(function() {
2    //set initial state.
3    $('#textbox1').val($(this).is(':checked'));
4
5    $('#checkbox1').change(function() {
6        if($(this).is(":checked")) {
7            var returnVal = confirm("Are you sure?");
8            $(this).attr("checked", returnVal);
9        }
10        $('#textbox1').val($(this).is(':checked'));        
11    });
12});

1$("checkbox").is(":checked")

1if($("#isAgeSelected").is(':checked'))
2    $("#txtAge").show();  // checked
3else
4    $("#txtAge").hide();  // unchecked
5