数字递增

function update_num(num,upid){

                var $up_n = $('#'+upid);

                var count = num;

                var number = 0;

                var str = '';

                var index_invite = setInterval(function() {

                    if (number > count) {

                        clearInterval(index_invite);

                        return false;

                    }

                    str = number;

                    if (str < 10) str = '0' + number;

                    number += 50;

                    $up_n.text(str);

}, 1);

            }

update_num("4000","update_number01");