var campos = [
document.querySelector('#data'),
document.querySelector('#valor'),
document.querySelector('#quantidade')
];
var tbody = document.querySelector('table tbody');
document.querySelector('.form').addEventListener('submit', function(event) {
var tr = document.createElement('tr');
campos.forEach(function(campo) {
var td = document.createElement('td');
td.textContent = campo.value;
tr.appendChild(td);
});
var tdVolume = document.createElement('td');
tdVolume.textContent = campos[1].value * campos[2].value;
tr.appendChild(tdVolume);
tbody.appendChild(tr);
campos[0].value = '';
campos[1].value = 1;
campos[2].value = 0;
campos[0].focus();
});