Can not validate a form with Struts

Question

I can not validate a form with this code. A popup does not appear.

<script type="text/javascript">
    function validate_login_form() {
        if (document.login_form.email.value == "" || document.login_form.password.value == "") {            
            alert('Some fields are empty');
            return false;
        }
        return true;
    }
</script>


<form id="login_form" action="login" method="post" onsubmit="return validate_login_form()">

    <s:textfield name="email" key="label.email" size="20" />
    <s:password name="password" key="label.password" size="20" />
    <s:submit method="execute" key="label.login" align="center" />

    <footer class="clearfix">
    <p><span class="info">?</span><a href="recover.jsp">Forgot password?</a>    <br />  <a class="reg" href="register.jsp">Register</a></p>
    </footer>
</form>

What is the reason?

It the content of function will be

alert('Some fields are empty');
return false;

then alert appears then something is with selectors?

Answer 1

Add name attribute to form tag

<form name="login_form"

The document element can reference a form by name like this

document.login_form or use document.forms[0] if you have only one form.