Javascript modifying prototypes

JS_object_prototype.js

function Person(name) {
  this.name = name;
  this.greeting = function() {
    console.log(`Hi I'm ${this.name}`);
  }
}

let person1 = new Person('Peter');
let person2 = new person1.constructor('Sarah');

Person.prototype.farewell = function() {
  console.log(`${this.name}: Bye for now!`);
}

person1.farewell();
// -> "Peter: Bye for now!"
person2.farewell();
// -> "Sarah: Bye for now!"