Asking for help on simple Javascript code regarding Inheritance

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Asking for help on simple Javascript code regarding Inheritance

grendall

function Person(firstName, lastName) {
        var _firstName = firstName;
        var _lastName = lastName;

    Person.prototype.__defineGetter__("firstName", function() {
       return _firstName; 
    });

    Person.prototype.__defineSetter__("firstName", function(value) {
        _firstName = value;
    });

    Person.prototype.__defineGetter__("lastName", function() {
        return _lastName;
    });

    Person.prototype.__defineSetter__("lastName", function(value) {
        _lastName = value;
    });
};

var p1 = new Person("John", "Doe");

console.log(p1.firstName); // Prints John
console.log(p1.lastName); // Prints Doe

function Dignitary() {

};

Dignitary.prototype = new Person(); // making Dignitary inherit Person
Dignitary.constructor = Dignitary; 

var d1 = new Dignitary("Jane", "Bimbo");
console.log(d1.firstName); // THIS IS COMING OUT UNDEFINED, WHAT AM I DOING WRONG?

Thanks in advance.

tech_soul8

This line of code effectively overwrites any previous values:

 Dignitary.prototype = new Person(); // making Dignitary inherit Person

any call to the Person() function will overwrite any previous values set. Adding this to the last line of the code proves it:

console.log(p1.firstName) // undefined

Probably you wanted to do something like:

      function Person()
      {
        //dummy function  

      }
      Person.prototype = {
         get firstName() {return this._firstName;},
         set firstName(x) {this._firstName = x;},
         get lastName() {return this._lastName;},
         set lastName(x) {this._lastName = x;}
      }

  var person = new Person;

  person.firstName = "Bruce";
  person.lastName = "Lee"
  console.log(person.firstName + " " + person.lastName);

  function Dignitary()
  {
     //dummy function
  }
  Dignitary.prototype = Person.prototype;

  var dignitary = new Dignitary;

  dignitary.firstName = "Johny";
  dignitary.lastName = "Bravo";
  console.log(dignitary.firstName + " " + dignitary.lastName);

Note that using the defineGetter and defineSetter functions is deprecated.

grendall

tech_soul8;1318469 wrote:
This line of code effectively overwrites any previous values:
 Dignitary.prototype = new Person(); // making Dignitary inherit Person
any call to the Person() function will overwrite any previous values set. Adding this to the last line of the code proves it:
console.log(p1.firstName) // undefined
Probably you wanted to do something like:
      function Person()
      {
        //dummy function  

      }
      Person.prototype = {
         get firstName() {return this._firstName;},
         set firstName(x) {this._firstName = x;},
         get lastName() {return this._lastName;},
         set lastName(x) {this._lastName = x;}
      }

  var person = new Person;

  person.firstName = "Bruce";
  person.lastName = "Lee"
  console.log(person.firstName + " " + person.lastName);

  function Dignitary()
  {
     //dummy function
  }
  Dignitary.prototype = Person.prototype;

  var dignitary = new Dignitary;

  dignitary.firstName = "Johny";
  dignitary.lastName = "Bravo";
  console.log(dignitary.firstName + " " + dignitary.lastName);
Note that using the defineGetter and defineSetter functions is deprecated.

Thanks for responding. I have to say though your response confuses me. I was creating a constructor that passed two parameters -- firstName and lastName, but your example did away with that.

Can you show me how your suggested solution would handle a constructor with two parameters? Thanks.

grendall

Oh, I take it back, I was thinking of a different sample I had elsewhere.

My question for you is that your Person.prototype definition used variables like firstName and lastName. Can you tell me where it would get those values? Thanks.

grendall

I think I should not check these responses when I'm very tired, haha!

I take back my questions, I now get what you were trying to convey in your sample. Thanks for your help!

tech_soul8

grendall;1318483 wrote:
Oh, I take it back, I was thinking of a different sample I had elsewhere.

My question for you is that your Person.prototype definition used variables like firstName and lastName. Can you tell me where it would get those values? Thanks.

...as I always try to explain things in details as best as I can/know, so...

Word about inheritance. Every object created with a constructor function will inherit properties from the prototype property of the constructor function. Like I said before the defineGetter and defineSetter (also lookupGetter and lookupSetter_) methods are considered deprecated. New syntax for accessor properties is introduced in ECMAScript 5 and it looks like:

get accessor property/I {//function body}
set accessor property/I {//function body}

You can also use Object.defineProperty(object,propName,descriptor). I recommend you read on these new methods. So, back to your question! I defined two dummy functions: Person and Dignitary. The prototype object has two getter and setter properties named firstName and lastName. Since JavaScript is a loosely typed language you can create your properties dynamically and that's what I did with the setter methods and the firstName and lastName properties.

Later you are using getter methods to get the value of newly created properties.

tech_soul8

grendall;1318485 wrote:
I think I should not check these responses when I'm very tired, haha!

I take back my questions, I now get what you were trying to convey in your sample. Thanks for your help!

Already answered, no problem!