Subj : Re: accessing methods of base class
To   : netscape.public.mozilla.jseng
From : Brendan Eich <brendan@meer.net>
Date : Sun Jul 20 2003 12:45 pm

mike caines wrote:

> Referring to example:
> 
> function One() {
>     this.toString = function() {return 'One';};
> }

It's better to share methods via the prototype, so:

function One() {}
One.prototype.toString = function () {return 'One';};

> 
> function Two() {
>     One.apply(this);
>     this.toString = function() {return <access One class toString> + '\n' +
> 'Two';}
> }
> Two.prototype = new One();

Likewise:

function Two() { /* you could call One.apply(this); here */ }
Two.prototype = new One;
Two.prototype.toString = function () {
   return One.prototype.toString() + '\nTwo';
}

> Is it somehow possible to access the original toString method of the base
> class once it has been overridden? So that the overriding version can
> 'append' to the original? (see example).

There are several ways; I've shown one above.  You could also give the 
base toString method a name in the global object, by declaring it as a 
top-level function (instead of writing a function expression).  Or in 
SpiderMonkey and Rhino, you could say this.__proto__.toString() in Two's 
toString body.

> Also, doesn't the Two.prototype = new One(); statement result in the One
> constructor being executed twice?

No.  Why would 'new One()' call the One constructor twice?

/be

.