clone element input JavaScript with null value

[gierg]

$(document).ready(function() {
            $('#btnAdd').click(function() {
                var num     = $('.clonedInput').length;
                var newNum  = new Number(num + 1);
 
                var newElem = $('#input' + num).cloneNode(true).attr('id', 'input' + newNum);
 
                newElem.children(':first').attr('id', 'name' + newNum).attr('name', 'name' + newNum);
                $('#input' + num).after(newElem);
                $('#btnDel').attr('disabled','');
 
                if (newNum == 5)
                    $('#btnAdd').attr('disabled','disabled');
            });

[Dormilich]

a little more description would be helpful.