Heya,
> You may want to use Crockford's factory pattern, rather than using any
> sort of constructor:
>
> function specialDateFactory() {
> var that = new Date();
>
> that.isEaster = function () {return ...},
> that.isLaborDay = function () {return ...},
>
> return that;
>
> }
The problem with that as written is that it creates separate isEaster
and isLaborDay functions for every single instance you create, each of
which eats memory:
var a = specialDateFactory();
var b = specialDateFactory();
alert(a.isEaster === b.isEaster); // "false"
You can avoid that:
var MoreDateFunctions = {
isEaster: function () {return ...},
isLaborDay: function () {return ...}
};
function specialDateFactory() {
return Object.extend(new Date(), MoreDateFunctions);
// Or, without Prototype's Object.extend:
// var fname, that;
// that = new Date();
// for (fname in MoreDateFunctions) {
// that[fname] = MoreDateFunctions[fname];
// }
// return that;
}
...but I'm not seeing much benefit at that point. I suppose it means
you haven't modified the Date prototype.
(BTW: Anyone tempted to create an ExtendedDate object using a Date
object as its prototype, think again, for some reason the spec
specifically disallows it in Section 15.9.5, and Firefox [and probably
others] implements the limitation.)
--
T.J. Crowder
tj / crowder software / com
Independent Software Engineer, consulting services available
On May 20, 4:07 pm, "P. Douglas Reeder" <reeder...@gmail.com> wrote:
> You may want to use Crockford's factory pattern, rather than using any
> sort of constructor:
>
> function specialDateFactory() {
> var that = new Date();
>
> that.isEaster = function () {return ...},
> that.isLaborDay = function () {return ...},
>
> return that;
>
> }
>
> You can get more sophisticated - creating a prototype object for
> special dates, with the functions defined on it, and using closures to
> protect it, but I can't write that off the top of my head...
>
> On May 20, 7:50 am, ColinFine <colin.f...@pace.com> wrote:
>
> > On May 20, 12:16 am, RobG <rg...@iinet.net.au> wrote:
>
> > > On May 19, 9:26 pm, ColinFine <colin.f...@pace.com> wrote:
>
> > > > This is a case when you really truly want just the facilities that
> > > > Javascript provides (prototypes rather than classes), and using
> > > > (pretend) classes makes it harder not easier.
>
> > > Yes, although some may argue that it is better to create a new object
> > > that has the required methods and leverages the methods of Date,
> > > rather than modifying a built-in object prototype,
>
> > Fair comment. But you are still talking about using Javascript's
> > prototype, rather than inventing classes. That was my point.
> > (I wouldn't have made this remark before I read Crockford's
> > "Javascript: The Good Parts" - that's opened my eyes to the strengths
> > that JS has. )
>
> > Colin
>
>
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