Problem in MaskedEditExtender with javascript

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Hi All,

i have 3 textboxes for area Code,phone number and Extention and each have
MaskedEditExten der associated with it.

i want that when the length of first text box reaches it's maxlength , focus
will be set to next textbox automatically, means i want auto tabbed fields.
for which i created java script function and associated it with OnKeyDown
and OnKeyUp event of TextBox. but it's not working and when i remove the
MaskedEditExten der it workes fine, Can anyone please guide me.


heare is my aspx code(here i am showing only 1 textbox but i have 3 textbox):-

<asp:TextBox ID="txtAreaCode " runat="server" Width="25px" MaxLength="3"
size="4" ></asp:TextBox>
<AjaxToolKit:Ma skedEditExtende r ID="meeAreaCode " runat="server"
TargetControlID ="txtAreaCod e"
AutoComplete="f alse" Mask="999" MaskType="None"
InputDirection= "LeftToRigh t"
ClearMaskOnLost Focus="False" PromptCharacter =" "
OnFocusCssClass ="MaskedEditFoc usNegative"
OnInvalidCssCla ss="MaskedEditF ocusNegative">


event association:-

String areaCodeDown = "javascript:Tab Next(this,'down ', " +
this.txtAreaCod e.MaxLength + ",)";
String areaCodeUp = "javascript:Tab Next(this,'up', " +
this.txtAreaCod e.MaxLength + ",'" + this.txtNumber. ClientID + "')";

this.txtAreaCod e.Attributes["OnKeyDown"] = areaCodeDown;
this.txtAreaCod e.Attributes["OnKeyUp"] = areaCodeUp;

Javascript function :-
var phone_field_len gth=0;
function TabNext(obj,eve nt,len,next_fie ld)
{

if (event == "down")
{

phone_field_len gth=obj.value.l ength;

}

else if (event == "up") {

if (obj.value.leng th != phone_field_len gth)
{

phone_field_len gth=obj.value.l ength;

if (phone_field_le ngth == len)
{

var next=document.g etElementById(n ext_field);

if(next != null)
next.focus();

}

}

}

}


Thanks