Why the checked and disabled prop return false when it is disabled and checked?

Here is my script of function to retrieve the properties of checkboxes:

var checkedCount = 0;

$('input.new-checkbox').each(function() {

     console.log('checked : ' + $(this).prop('checked')); // returned false
     console.log('disabled : ' + $(this).prop('disabled')); // returned false

     console.log('checked : ' + this.checked); // returned false
     console.log('disabled : ' + $(this).attr('disabled')); // returned undefined

     console.log('checked : ' + $(this).is(':checked')); // returned false

     console.log('disabled : ' + $(this).attr('disabled')); // returned undefined            
     console.log('checked : ' + $(this).attr('checked')); // returned undefined

     if($(this).prop('checked') == true)
     {
            checkedCount = checkedCount + 1;                    
     }

});

Here is the script of function how I disable and check a checkbox, where arrayA is an array:

$('input.new-checkbox').each(function() {

        for(var i=0; i<arrayA.length; i++)
        {                               
            if($(this).val() == arrayA[i])
            {           
                // set the checkbox checked
                $(this).prop('checked', true);

                // disable the checkbox
                $(this).prop('disabled', true);

            }                               

        }

    });

I check each checkbox if its value equals to the value in array, then set the checkbox checked and disable it.

When I click/check the checkbox, it returns me the state of the prop('checked') and prop('disabled') correctly. But when it already been disabled and checked, it gives me 'false' for both 'checked' and 'disabled' properties.

Anybody know why is this happened?