slender2_nameEditor.js

function NameEditor() {
  return `
    <div class="nameEditor">
      <div>Enter you name:</div>
      <input onKeyUp="NameEditor.onKeyUp(this)" />
      <div>
        Hello, <span></span>
      </div>
    </div>
  `;
}

NameEditor.onKeyUp = (input) => {
  input.nextElementSibling.querySelector('span').innerText = input.value;
};