asp.net 屏蔽 只能 是数字

 //数字字符
       public static string KeepNum(string str)
       {
           char[] tmp = new char[str.Length];
           char[] s = str.ToCharArray();
           for (int i = 0, j = 0; i < str.Length; i++)
           {
               if (s[i] >= '0' && s[i] <= '9')
               {
                   tmp[j] = s[i];
                   j++;
               }
           }
           return new string(tmp);
       }
<input type="text" id="mobile" runat="server" maxlength="12" onkeyup="value=value.replace(/[^\d]/g,'')" />