dom-owner.js

const data = {};
window.getData = name => {
  const item = data[name];
  return item && item.value;
}
window.setData = (owner, name, value) => {
  const previous = data[name];

  if (!previous || previous.owner === owner) {
    data[name] = {
      owner,
      name,
      value,
    };

    window.dispatchEvent(new CustomEvent('changed-data', {
      detail: {
        name,
        previous: previous && previous.value,
        current: value,
      },
    }));
  }
};