const cell = {
  title: '',
  value: ''
}
const handler = {
  set(target, property, value) {
    if (property === "title") {
      if (typeof value !== "string") {
        throw new Error("title must be a string.");
      }
    }
    target[property] = value;
  }
};

const proxyCell = new Proxy(cell, handler);
cell.title = 123; // error