var id = function(id) {
        return document.getElementById(id);
    }

    function submit_survey() {
        var err_el = id('error-msg');
        var form   = id('submit-survey');

        var inputs_name = {
            park: ['radio', 'Park'],
            email: ['id', 'Email address'],
            fullname: ['id', 'Your name'],
            ticketnumber: ['id', 'Ticket number'],
            bibnumber: ['id', 'Bib Number']
        };
        var err_msg = [];

        for(var i in inputs_name) {
            var info     = inputs_name[i];
            var input    = id(i);
            var is_radio = info[0] == 'radio';
            var val      = '';

            if (is_radio) {
                var radios        = form.elements[i];
                var radio_checked = '';

                for(var i=radios.length; --i; )
                    if (radios[i].checked) {
                        radio_checked = 'true';
                        break;
                    }

                val = radio_checked;
            }

            else {
                var val = input.value;
            }

            if (val.replace(/^\s+|\s+$/g, '') == '') {
                err_msg.push('<strong>' + info[1] + '</strong> is required. ');
            }

            if (i == 'email' && !/^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/.test(val)) {
                err_msg.push('<strong>' + info[1] + '</strong> is invalid email address. ');
            }

        }

        if (err_msg.length) {
            err_el.style.display = 'block';
            err_el.getElementsByTagName('ul')[0].innerHTML = '<li>' + err_msg.join('</li><li>') + '</li>';
            return false;
        }

        return true;
    }