Untitled

<html>
    <head>
    <title> The Age Calculator</title>
    </head>
<body>
    <script language="JavaScript">
function CalculateAge()
{
var birthyear = document.form1.txt.value;
var currentyear  = new Date();
var age   = currentyear.getFullYear();
document.write('They are either ' + (age-birthyear)+ ' or ' + (age-birthyear - 1));
 }
    </script>
        <form name=form1>
            Enter the Birth Year
           <input type="text" name="txt" size=10>
           <br>
           <input type="button" value="Calculate" onClick='CalculateAge();'>
        </form>
</body>
</html>