var W3CDOM = (document.getElementsByTagName && document.createElement);

window.onload = function () {
        document.forms[0].onsubmit = function () {
                return validate()
        }
}

function validate() {
        validForm = true;
        firstError = null;
        errorstring = '';
        var x = document.forms[0].elements;
        for (var i=0;i<x.length;i++) {
                if (!x[i].value)
                        writeError(x[i],'required');
        }
        if (x['email'].value.indexOf('@') == -1)
                writeError(x['email'],'invalid email');
        if (!W3CDOM)
                alert(errorstring);
        if (firstError)
                firstError.focus();
        if (validForm)
                document.forms[0].submit();
        return false;
}

function writeError(obj,message) {
        validForm = false;
        if (obj.hasError) return;
        if (W3CDOM) {
                obj.className += ' error';
                obj.onchange = removeError;
                var sp = document.createElement('span');
                sp.className = 'error';
                sp.appendChild(document.createTextNode(message));
                obj.parentNode.appendChild(sp);
                obj.hasError = sp;
        }
        else {
                errorstring += obj.name + ': ' + message + '\n';
                obj.hasError = true;
        }
        if (!firstError)
                firstError = obj;
}

function removeError()
{
        this.className = this.className.substring(0,this.className.lastIndexOf(' '));
        this.parentNode.removeChild(this.hasError);
        this.hasError = null;
        this.onchange = null;
}