Question

If I have a function say:

var my_function = function()
  {
  }

If the function is not called, it is not taking up memory, it is just text sitting in memory.

However if you call it by say…

function_instance = new my_function();

It is instantiated is a sort of way, and the variables and methods it contains are loaded into memory.

Is this a way to represent a class/object model similar to C++?

Is my interpretation correct?

Answer 1

“a way to represent a class/object model similar to C++” would be through the use of prototypes.

As Kevin M pointed out, you can use the this keyword to create instance variables in a function, like so:

var my_function(foo)
{
  this.foo = foo;
  this.bar = function()
  {
    // bar-ing here
  }
}

The problem however, that whenever you instantiate my_function(), a new instance of the my_function.bar function is also created. Enter prototypes:

var barPrototype = { "bar" : function()
  {
    // bar-ing here
  }
};

var my_function(foo)
{
  this.foo = foo;
}
my_function.prototype = barPrototype;

So, to sum it all up, the prototype keyword can be used to create function-specific, inheritable properties that are analoguous to C++’s member functions. Member functions of C++ aren’t instantiated for each instance of a class. Instead, the compiler adds a this pointer to the function’s parameters; this pointer points to the instance that the member function is called on.

More JSey fun to be had here: http://javascript.infogami.com/Javascript_in_Ten_Minutes