Factory Functions & Singleton Pattern

What feature is demonstrated by the Object.defineProperty() usage?

function createPerson(name, age) {
  const person = {
    name,
    age,
    greet() {
      return `Hello, I'm ${this.name}`;
    }
  };
  
  Object.defineProperty(person, 'birthYear', {
    get() {
      const currentYear = new Date().getFullYear();
      return currentYear - this.age;
    }
  });
  
  return person;
}

Data validation
Method binding
Computed properties
This demonstrates computed properties via Object.defineProperty(): 1) It creates a property that's calculated on-demand rather than stored, 2) The birthYear property is derived from other data (age) and external state (current year), 3) It will always return an up-to-date value as age or the current year changes, 4) It saves memory by not storing data that can be derived, 5) This approach is useful for creating properties that need to stay in sync with other data, 6) It demonstrates how factory functions can leverage advanced property definitions.
Property locking

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