class Person {
	
	constructor (firstName, lastName, dateOfBirth) {
		this._firstName   = firstName;
		this._lastName    = lastName;
		// expected to be an instance of Date class
		this._dateOfBirth = dateOfBirth;
	}
	
	set firstName (newValue) {
		this._firstName = newValue;
	}
	get firstName() {
		return this._firstName;
	}
	
	set lastName (newValue) {
		this._lastName = newValue;
	}
	get lastName () {
		return this._lastName;
	}
	
	get fullName () {
		return this._firstName + ' ' + this._lastName;
	}
	
	set fullName (newValue) {
		console.error('You cannot set the fullName, change firstName and lastName seperately instead.');
	}
	
	// the age calculation will fail, if dateOfBirth won't contain a Date instance
	get age() {
		// get the current Date
		let currentDate = new Date();
		// split start date components
		let syear       = this._dateOfBirth.getYear();
		let smonth      = this._dateOfBirth.getMonth();
		let sday        = this._dateOfBirth.getDate();
		// split end date components
		let eyear       = currentDate.getYear();
		let emonth      = currentDate.getMonth();
		let eday        = currentDate.getDate();
		
		// normalize day of month to 30, if bigger
		if (sday === 31) sday = 30;
		if (eday === 31) eday = 30;
        // (don't change February 28 or February 29)
		
		// linearize the components to a harmonized value range
		let startDateLinearized = (eday + emonth * 30 + eyear * 360);
		let endDateLinearized   = (sday + smonth * 30 + syear * 360);
		// return the difference fraction without the fraction part
		return Math.floor((startDateLinearized - endDateLinearized) / 360);
	}
	
	set age(newValue) {
		console.error('You cannot set the age, its calculated, change dateOfBirth instead.');
	}
}

var andre = new Person('André','Kleinschmidt',new Date('1981-11-27'));
console.log(andre.firstName + ' is ' + andre.age + ' years old.');