Object creation question

[Pepejeria]

I am using this syntax to create an object:

carObject = {
	model : "Volvo",
	color : "blue",
	outputModel : function()
	{
		alert("Modelname is: " + this.model)
	}
};

carObject.outputModel(); // alerts "Modelname is Volvo"

Lets say i would like to add a new property, called brand, thats is equal to model. Can anyone please explain why this doesnt work?

carObject = {
	model : "Volvo",
	color : "blue",
	brand : this.model, 
	outputModel : function()
	{
		alert("Modelname is: " + this.brand)
	}
};

carObject.outputModel(); // alerts "Modelname is undefined"

[vikrantkorde]

Hi Pepejeria,
I can;t tell you why the above code is not working but this code works

  carObject = {
      model : "Volvo",
      brand : ""+this.model+"",
      color : "blue",
      outputModel : function()
      {
          this.setval();
          alert("Modelname is: " + this.brand)
      },
      setval : function() {
          this.brand=this.model;
      }
  };
  
  carObject.outputModel(); // alerts "Modelname is Volvo"

What i can guess is that you can't access the value of the variable in the variable area itself, rather it can be accessed only from functions.

[7stud]

The bible says:

A costructor is a js function with two special features:

--The function is invoked using the new operator.
--The function is passed a reference to a newly created, empty object as the value of the this keyword, and it is responsible for performing initialization for that new object. ("Javascript: The Definitive Guide" (Flanagan))

On the other hand, what you are using is an 'object literal', and apparently the assigning of an object literal to a variable name does not cause the 'this' keyword for that variable name to be passed to the object literal.

However, all function are passed the 'this' keyword--even global functions. Global functions are really properties of the window object, so in a global function, this refers to the window object. For other functions, this refers to the calling object.

[stereofrog]

Lets say i would like to add a new property, called brand, thats is equal to model. Can anyone please explain why this doesnt work?

carObject = {
	model : "Volvo",
	color : "blue",
	brand : this.model, 
	outputModel : function()
	{
		alert("Modelname is: " + this.brand)
	}
};

carObject.outputModel(); // alerts "Modelname is undefined"

"this" is a pointer to the "execution context", i.e. object the current function was called for. In javascript, "called for" means one of the following:

-- function was called using dot notation: object.func()
-- function is a constructor: object = new func();
-- function is called indirectly via call() or apply()

Since neither takes place in given case, this takes a default value, namely "window" (in browser).

The common way to achieve this is to use constructors:

function carObject() {
	this.model =  "Volvo";
	this.brand = this.model;
	this.outputModel = function()
	{
		alert("Modelname is: " + this.brand)
	}
}

alert((new carObject()).brand)

"Delayed initialization" method shown by vikrantkorde can be also useful:

  carObject = {
      model : "Volvo",
      outputModel : function()
      {
	  	if(typeof(this.brand) == "undefined")
			this.brand = this.model;
          alert("Modelname is: " + this.brand)
      }
  }
  
  carObject.outputModel();

[Pepejeria]

Thank you for the answers, you guys rock