Set Maxlength to TextArea

Question: I want to set maximum length to the textarea. I am using following code for the same,but it is not working,

<textarea name="txtDescription" cols=10 rows=3 maxlength=50></textarea>

But it is not working,it takes characters beyond 50.

This solution is re-usable for all text areas via one function and
it doesn't inform the user that he/she is typing too many characters, it prevents them from doing so, sort of like maxlength

The Function:

<script language="javascript" type="text/javascript">
<!--
function imposeMaxLength(Object, MaxLen)
{
  return (Object.value.length <= MaxLen);
}
-->
</script>

Implementation:

<textarea name="myName" onkeypress="return imposeMaxLength(this, 15);" ><textarea>

HTML forms TextArea maxLength restrict entry