How to find control in formview from javascript

[AkAlan]

I'm trying to retrieve the value of a text box "txtDrumNumber" so I can run a validation script. I can't seem to get the correct method for this. Here is what has been suggested but didn't work.

<script type="text/javascript">
function isValidDrumNumber(sender, args) {
var DrumNumber = fvAddNewDrum.FormviewRow.FindControl("txtDrumNumber").ClientID;
var DrumString = DrumNumber.value;
if (DrumString.length = 11) {
return true;
}
else {
DrumNumber.focus();
args.IsValid = false;
return false;
}
}
</script>

[abduraooft]

var value=document.getElementById('myinput');
alert(value);

<input type="text" name="myinput" id="myinput">

The above should work in all cases(with no major errors in markup).