js控制asp.net服务器端控件textbox设置为多行时输入字符长度

<script language="javascript">

    <!--

        function MaxLength(field,maxlimit)

        {

             var str = field.value.replace(/[^\x00-\xff]/g,"**").length;

             //alert(str);

             var tempString=field.value;

             var tt="";

             if(str > maxlimit)

             {

                 for(var i=0;i<maxlimit;i++)

                 {

                    if(tt.replace(/[^\x00-\xff]/g,"**").length < maxlimit)

                    tt = tempString.substr(0,i+1);

                    else

                    break;

                 }

                 if(tt.replace(/[^\x00-\xff]/g,"**").length > maxlimit)

                 tt=tt.substr(0,tt.length-1);

                 field.value = tt;

               }

               else

               {

                     ;

               }

         }

    -->

</script>  

 <asp:TextBox ID="TextBox1" runat="server" TextMode="MultiLine"  Width="50%"  onpropertychange="MaxLength(this,100)"></asp:TextBox>