มิกซ์อิน (ลองทำความรู้จัก) — นำกลับมาใช้ใหม่โดยไม่สร้างลำดับชั้นลึก

// A simple mixin: adds timestamp helpers
const timeMixin = {
  setCreatedNow: function () {
    this.createdAt = new Date(0); // fixed for demo output
  },
  ageMs: function () {
    if (!this.createdAt) return 0;
    return 1234; // fixed number for a stable demo
  }
};

console.log("mixin keys:", Object.keys(timeMixin));

// Apply the mixin to all instances via the prototype
class Note {
  constructor(text) {
    this.text = text;
  }
}

// Copy methods to the prototype so every instance can use them
Object.assign(Note.prototype, timeMixin);

const n = new Note("hello");
n.setCreatedNow();
console.log("ageMs:", n.ageMs());

// You can also mix into just one instance
const single = { name: "one" };
Object.assign(single, timeMixin);
single.setCreatedNow();
console.log("single ageMs:", single.ageMs());

// Factory + mixin: build an object then add abilities
function makeUser(name) {
  return { name: name };
}

const u = makeUser("Ayla");
Object.assign(u, timeMixin);
u.setCreatedNow();
console.log("user ageMs:", u.ageMs());