A specific length of digit entry javascript validation

I need a limited length of digits validation using javascript function.
Let's say a format with only 8 digits for a textbox. What would be a simple way to do it?
I did some validations but never did for a limited length.
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Alfred A.Commented:
You can use CustomValidator Control if you want.   You can use it for client-side validation.  Check the sample code below:
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head2" runat="server">
     <title>Validate Text Box</title>
     <script language="javascript" type="text/javascript">
          function ValidateTextBox(source, arguments) {
             var data = arguments.Value.split('');
             //start by setting false
             arguments.IsValid = false;
             //check length
             if(data.length != 8) return;
             arguments.IsValid = true;
<body style="font-family: Arial">
    <form id="form1" runat="server">
         <asp:TextBox ID="txtTest" runat="server"></asp:TextBox>
         <asp:CustomValidator ID="txtTestCustomValidator" runat="server"
                Text="*" ToolTip="Only 8 digits allowed."
                ErrorMessage="Only 8 digits allowed."
         <asp:Button ID="ButtonSubmit" runat="server" Text="Submit" />

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Use regex to match..


input control
<input type="text" id="TextBox1" onblur="chkTxtVals();"/>

function chkTxtVals() {
	if (!document.getElementById('TextBox1').value.match(/\d{8}/))
		alert('value must be 8 digits');

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if it's at least 8 digits then use this regex


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you can always set the maxlength property of the textbox to 8

if only javascript needs to be used:

if the string is passed to the javascript function, use
if (str.length > 8)
    return str.substring(0,8);

and add the attribute to the textbox for onkeyup or onchange event..or u can just assign the attribute "javascript:if(str.length>8) return str.substring(0,8);" for the onkeyup or onchange events...

minglelinchAuthor Commented:
I tried the follow code, the alert box never popup ......

<asp:Button ID="btnSave" runat="server" Text="Save" OnClientClick="return chkVals();"  OnClick="btnSave_Click"/>  

function chkVals() {
         var txtvalue = document.getElementById("<%=txtCNum.ClientID%>").value;
         if (!txtvalue.match(/\d{8}/)) {
                     alert(CNum must be 8 digits for saving');
      return false;
i see only two issues here
apostraphe inside alert is missing: alert('
and function ending flower bracket is mising: }
i agree that other than the missing ' everything seems to be ok.

btw if you want btnSave_Click to be fired on the server when the value is valid you might want to do it this way..
OnClientClick="if (!chkVals()) return false;"

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minglelinchAuthor Commented:
I tried all of these. It's not working. Then I just checked str.length and give alert message in javascript function, and it is working. Thanks for all the comments.
So you need 8 characters and not digits? A "digit" would be a numeral character. If your input doesn't have to be restrained to digits then sure you can use length.
minglelinchAuthor Commented:
I have restricted any character input at KeyPress event, only allowed digits entry, and then restricted input entry length to achive my purpose.
Tom KnowltonWeb developerCommented:
I've requested that this question be deleted for the following reason:

This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.
minglelinchAuthor Commented:
Those comments are very good. I would like to have them visible to me for future references.
minglelinchAuthor Commented:
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