manero

<html>
    <head>
        <script language="text/javascript">
            function changeText(element_id, text) {
                var el = document.getElementById(element_id);

                window.alert(el);

                if (el !== null) {
                    el.value = text;
                    window.alert("changed value?");
                    return true;
                } else {
                    window.alert("el is null");
                    return false;
                }
            }
        </script>
    </head>

    <body>
        <p><input type="text" name="fooName" id="fooInput" /></p>
        <p><a href="#" onclick="javascript:changeText('fooName', 'success');">Click Here</a></p>
    </body>

</html>