const days = [
  "Monday",
  "Tuesday",
  "Wednesday",
  "Thursday",
  "Friday",
  "Saturday",
  "Sunday",
];

function proxy(target) {
  return new Proxy(target, {
    get: (target, property, receiver) => {
      const result = Reflect.get(target, property, receiver);

      if (days.includes(result)) {
        return {
          toString: () => result,
          valueOf: () => result,
          length: "24 hours",
        };
      }

      return result;
    },
    set: (target, property, receiver) => {
      return Reflect.set(target, property, receiver);
    },
  });
}

with (proxy(globalThis)) {
  x = "Monday";
  y = "Something Else";
  z = "Saturday";
  
  console.log(x.length, y.length, z.length);
}