javascript input只输入数字和字母

 <input type="text" placeholder="请输入您的用户名...">
 <script type="text/javascript">
         $("input[name='username']").bind('input',function(){
             var pattern = new RegExp("[^a-zA-z1-9]");
             var rs = '';
             var str = $(this).val();

             for (var i=0;i< str.length;++i){
                 rs = rs + str.substr(i, 1).replace(pattern,'');
             }

             $(this).val(rs);
         });
 </script>