getter setter for age problem
function User(name, birthday) { this.name = name; this.birthday = birthday; Object.defineProperty(this, "age", { get() { let todayYear = new Date().getFullYear(); return todayYear - this.birthday.getFullYear(); } }); } let john = new User("John", new Date(1992, 6, 1)); console.log(john.birthday); console.log(john.age);