Bug 1028789 - [Sora]There is no character counter inside STK submenus

What about:

var charactersLeft = (maxLength - inputLength);

self.icc_input_btn.textContent = _('ok') + ' (' + charactersLeft + ')';
self.icc_input_box.classList.toggle('full', charactersLeft);

if (charactersLeft === 0) {
  navigator.vibrate([500]);
}