Question

What's the output?

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

const member = new Person('Lydia', 'Hallie');
Person.getFullName = function() {
  return `${this.firstName} ${this.lastName}`;
};

console.log(member.getFullName());

• A: TypeError
• B: SyntaxError
• C: Lydia Hallie
• D: undefined undefined

Answer 1

Answer: A

In JavaScript, functions are objects, and therefore, the method getFullName gets added to the constructor function object itself. For that reason, we can call Person.getFullName(), but member.getFullName throws a TypeError.

If you want a method to be available to all object instances, you have to add it to the prototype property:

Person.prototype.getFullName = function() {
  return `${this.firstName} ${this.lastName}`;
};