Inheritance in JS

inheritance.js

function Person(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}

Person.prototype.fullName = function() {
 return this.firstName + " " + this.lastName; 
};

function Teacher(roomNumber) {
  Person.call(this, firstName, lastName);
  this.roomNumber = roomNumber;
}

Teacher.prototype = Object.create(Person.prototype);