自动验证textbox输入

验证textbox输入：
   
function checkKeyCode(reg)
 {
  var keyCode = window.event.keyCode;
  var srcElem = event.srcElement
  var oSel = document.selection.createRange()
  var srcRange = srcElem.createTextRange()
  oSel.setEndPoint("StartToStart", srcRange)
  var num = oSel.text + String.fromCharCode(keyCode) + srcRange.text.substr(oSel.text.length)
        if(keyCode == 13)
        {
            document.getElementById("ChangePasswordPushButton").click();
            window.event.returnValue = 0;
        }
        else
        {
      event.returnValue = reg.test(num);
  }
 }

用法：
<asp:TextBox ID="txtUserID" MaxLength="25" runat="server" Width="158px" onkeypress="checkKeyCode(/^[A-Za-z0-9]+$/)"></asp:TextBox>