JS constructor without class and with class - prototype

prototype.js

// Object prototype
//	|
// Person prototype
//	|
// Person instance 		ex) john

// Constructor
function Person(firstName, lastName, dob) {
	this.firstName = firstName;
	this.lastName = lastName;
	this.birthday = new Date(dob);
	// this.calculateAge = function () {
	// 	const diff = Date.now() - this.birthday.getTime();
	// 	const ageDate = new Date(diff);
	// 	return Math.abs(ageDate.getUTCFullYear() - 1970);
	// };
}

// Calculate age
Person.prototype.calculateAge = function () {
	const diff = Date.now() - this.birthday.getTime();
	const ageDate = new Date(diff);
	return Math.abs(ageDate.getUTCFullYear() - 1970);
};

const john = new Person('John', 'Doe', '8-12-90');
const mary = new Person('Mary', 'Johnson', 'March 20 1978');

console.log(mary);

// with class -------------------------------------------------------------------------

class Person {
	constructor(firstName, lastName, dob) {
		this.firstName = firstName;
		this.lastName = lastName;
		this.birthday = new Date(dob);
	}

	calculateAge() {
		const diff = Date.now() - this.birthday.getTime();
		const ageDate = new Date(diff);
		return Math.abs(ageDate.getUTCFullYear() - 1970);
	}
}

const john = new Person('John', 'Doe', '8-12-90');
const mary = new Person('Mary', 'Johnson', 'March 20 1978');

console.log(mary);