text: function displayError(message) {
    displayError.numTimesExecuted++
    alert(message)
  }
  displayError.numTimesExecuted = 0
  
  /* Class Person. */
  
  function Person(name, age) {
    this.name = name
    this.age = age
  }
  Person.prototype = {
    getName: function() {
      return this.name
    },
    getAge: function() {
      return this.age
    },
  }
  
  /* Instantiate the class. */
  
  var alice = new Person("Alice", 93)
  var bill = new Person("Bill", 30)
  
  /* Modify the class. */
  
  Person.prototype.getGreeting = function() {
    return "Hi " + this.getName() + "!"
  }
  
  /* Modify a specific instance. */
  
  alice.displayGreeting = function() {
    alert(this.getGreeting())
  }
  