Extending javascript literal object

Question

Why JohnDoe.whoAreYou() does return undefined ?:

<html>
<head>
</head>

<body>
  <script>
    var JohnDoe = {
        //public property
        firstName: "John",
        lastName: "Doe",

        //public method
        whoAreYou: function() {
          alert( "I am literal object and my name is " + this.toString());
        },
        whatIsYourAge: function() {
          alert("My age is " + this.Age);
        }               
    };    
  </script>

  <script>
    JohnDoe.Age = 10;
    JohnDoe.toString = function() {this.firstName + " " + this.lastName};
    JohnDoe.whoAreYou();    
    JohnDoe.whatIsYourAge();
  </script>

</body>
</html>

for starters, you want this: JohnDoe.toString = function() { return this.firstName + " " + this.lastName} — Brian Driscoll
– Brian Driscoll, Commented Nov 22, 2010 at 17:28

Darin Dimitrov · Accepted Answer · 2010-11-22 17:27:41Z

4

Because you aren't returning anything from this function. Try like this:

JohnDoe.toString = function() {
    return this.firstName + " " + this.lastName;
};

answered Nov 22, 2010 at 17:27

Darin Dimitrov

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1 Comment

Rebol Tutorial Over a year ago

Thanks I'm too used to rebol that doesn't need return.

Ivo Wetzel · Accepted Answer · 2010-11-22 17:33:05Z

3

Your approach to creating objects is very limiting.

You should rather create a new instance from a constructor and pass in the values to that function.

function User(firstName, lastName, age) {
   this.firstName = firstName;
   this.lastName = lastName;
   this.age = age;
   // set name etc here
}

User.prototype.toString = function() {
    // Note the "return" so this function actual returns something
    return this.firstName + " " + this.lastName; 
}
User.prototype.whoAreYou = function() {
    alert( "I am literal object and my name is " + this.toString());
}

var JohnDoe = new User("John", "Doe", 10); 
JohnDoe.whoAreYou();


var someoneElse = new User("Someone", "Else", 15); 
someoneElse.whoAreYou();

answered Nov 22, 2010 at 17:33

Ivo Wetzel

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3 Comments

Pointy Over a year ago

uhh ... if he puts a "return" keyword in his "toString" function it'll all work just fine ... when he calls the functions as property references off his "JohnDoe" object, then this will indeed refer to that object

Ivo Wetzel Over a year ago

@Pointy yeah, guess I misread the question, guess I'm to tired :/ Reworked it to give some advice on object creation.

Rebol Tutorial Over a year ago

Thanks Ivo, I'm not considering prototype yet but I will then I'll look at your sample :)

Pointy · Accepted Answer · 2010-11-22 17:27:41Z

1

Because you forgot to return the value from the "toString" function you defined.

answered Nov 22, 2010 at 17:27

Pointy

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