slender3_NameEditor3.js

const nameElems = {};

function getNameElems(id) {
  return nameElems[id] || (
    nameElems[id] = document.getElementsByClassName(`nameEditor__name-${id}`)
  );
}

NameEditor.onKeyUp = (input, id) => {
  for (const elem of getNameElems(id)) {
    elem.innerText = input.value;
  }
};