function_prototype.js

var secret = 'Not telling!';
function Person(name){
  this.name = name;
  this.greeting = 'Hello!';
}

Person.prototype.sayGreeting = function(){
  return this.name + ' says, "' + this.greeting + '"';
};

Person.prototype.getSecret = function(){
  return secret;
};

var jane = new Person('Jane');
jane.sayGreeting(); // Jane says, "Hello!"
jane.getSecret();  // Not telling!

expect(jane instanceof Person).toBe(true);