Q:

jquery check-uncheck checkbox

When I click on Problem, both check boxes must select/deselect. I want to select and deselect check boxes for multiple time. It works only for selecting and then deselecting (2 times) and then is not working any more.

My code: 
 $(document).ready(function() {
        $('#CHECK-ALL').click(function() {
            if ($(this).is(':checked')) {
                $('#P').attr('checked',true);                
            } else {
                $('#P').attr('checked',false);                
            }
        });
    });

A:

You're using the wrong method, you should be using prop
$(document).ready(function() {
    $('#CHECK-ALL').click(function() {
        if ($(this).is(':checked')) {
            $('#P').prop('checked',true);                
        } else {
            $('#P').prop('checked',false);                
        }
    });
});

Your code could be reduced to
$('#CHECK-ALL').click(function() {
    $('#P').prop('checked', this.checked);                
});

When you set the attribute, it works fine, but it doesn't change the property, so the next time you check $(this).is(':checked') it's still unchecked, as that checks the property, not the attribute, which is why it's not working.

