validade form with native JS

checkform.js

function validadeForm() {

    var lang = document.documentElement.lang;

    switch (lang)
    {
        case 'pt':
            var language = 'pt',
                error_message = 'Campo obrigatório.'
            break;
        case 'en':
            var language = 'en',
                error_message = 'Mandatory Field.'
            break;
    }

    var formField = document.querySelectorAll('input');

    formField.forEach(function (el,i)
    {
        if (el.value.trim() == '' && el.required == true || (el.type == 'checkbox' && el.checked == false))
        {
            errorMessage(el,error_message);
        }

        el.addEventListener('input', () => {

            if (el.value.trim() == '' && el.required == true || (el.type == 'checkbox' && el.checked == false))
            {
                errorMessage(el,error_message);
            }
            else
            {
                var fieldParent = el.parentNode,
                    childnode = fieldParent.querySelector('.errorMessage');

                if (fieldParent.contains(childnode) == true)
                {
                    fieldParent.classList.remove('has-error');
                    fieldParent.removeChild(childnode);
                }
            }
        });
    });
}

function errorMessage(el,errorMessage) {

    document.addEventListener('invalid', (function () {
        return function (e) {
            e.preventDefault();
            e.stopPropagation();
        };
    })(), true);

    var fieldParent = el.parentNode,
        childnode = fieldParent.querySelector('.errorMessage');

    if (fieldParent.contains(childnode) == false) {

        var errorEl = document.createElement("div");

        errorEl.className = "errorMessage";
        errorEl.innerHTML = '<span>' + errorMessage + '</span>';

        el.parentNode.classList.add('has-error');
        el.parentNode.appendChild(errorEl);
    }
}

// function peaSendMail(data) {
//     $.post('pea/peaSendMail.php', data, function(res) {
//         alert(res.data);
//         if (res.status == 0) {
//             $('#pea-contact')[0].reset();
//         }
//     }, 'json');
// }