Overriding a constructor

[CAFxX]

I'm trying to solve a problem with my code but can't come up with a
solution.
Suppose I have a "class" A with its constructor (that I can't modify
directly)

function A() {
/* constructor code */
};
what I'd like to do is to make the constructor call a certain function I
specify before returning, i.e.

function A() {
/* constructor code */
someFunction();
};

is this possible?
CAFxX

[CAFxX]

Just to clarify, the aim is that all the code that is instantiating an
instance of "class" A, perform the call to someFunction() without rewrites.

CAFxX ha scritto:

I'm trying to solve a problem with my code but can't come up with a
solution.
Suppose I have a "class" A with its constructor (that I can't modify
directly)

function A() {
/* constructor code */
};
what I'd like to do is to make the constructor call a certain function I
specify before returning, i.e.

function A() {
/* constructor code */
someFunction();
};

is this possible?
CAFxX

[sheldonlg]

CAFxX wrote:

I'm trying to solve a problem with my code but can't come up with a
solution.
Suppose I have a "class" A with its constructor (that I can't modify
directly)

function A() {
/* constructor code */
};
what I'd like to do is to make the constructor call a certain function I
specify before returning, i.e.

function A() {
/* constructor code */
someFunction();
};

is this possible?
CAFxX

Why not have a second class that extends the first class. In the second
class you could have a method A and in its constructor you could have
$this->A();

[sheldonlg]

sheldonlg wrote:

CAFxX wrote:

>I'm trying to solve a problem with my code but can't come up with a
solution.
Suppose I have a "class" A with its constructor (that I can't modify
directly)

function A() {
/* constructor code */
};
what I'd like to do is to make the constructor call a certain function
I specify before returning, i.e.

function A() {
/* constructor code */
someFunction();
};

is this possible?
CAFxX

Why not have a second class that extends the first class. In the second
class you could have a method A and in its constructor you could have
$this->A();

Oops, I thought I was in a different newsgroup. I don't know about
classes in javascript.

[Joost Diepenmaat]

CAFxX <us********@REMOVEMEcafxx.cjb.netwrites:

I'm trying to solve a problem with my code but can't come up with a
solution.
Suppose I have a "class" A with its constructor (that I can't modify
directly)

function A() {
/* constructor code */
};
what I'd like to do is to make the constructor call a certain function
I specify before returning, i.e.

function A() {
/* constructor code */
someFunction();
};

is this possible?
CAFxX

You mean you want to replace the constructor A at runtime with some other
function that calls the original A and then adds some more
functionality?

var OldA = A;
A = function() {
OldA.apply(this,arguments);
// do new stuff here
};

// copy any properties set on OldA
for (p in OldA) {
if (OldA.hasOwnProperty(p)) {
A[p] = OldA[p];
}
// this may fix some potential issues
// and break some others
A.prototype.constructor = A;
}

If the original code tries hard enough, it can always detect that (and
break because) the constructor been replaced, and if there are already
instances of A around at the time the new constructor is created those
instances will be instanceOf OldA, not A.

see also:

http://joost.zeekat.nl/constructors-...confusing.html

HTH,
Joost.

--
Joost Diepenmaat | blog: http://joost.zeekat.nl/ | work: http://zeekat.nl/

[Gregor Kofler]

sheldonlg meinte:

Oops, I thought I was in a different newsgroup. I don't know about
classes in javascript.

No one knows.

Gregor
--
http://photo.gregorkofler.at ::: Landschafts- und Reisefotografie
http://web.gregorkofler.com ::: meine JS-Spielwiese
http://www.image2d.com ::: Bildagentur für den alpinen Raum

[Thomas 'PointedEars' Lahn]

Gregor Kofler wrote:

sheldonlg meinte:

>Oops, I thought I was in a different newsgroup. I don't know about
classes in javascript.

No one knows.

That depends on what is meant by "javascript" ;-)
SCNR

PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f8*******************@news.demon.co.uk>

[CAFxX]

Right, sarcasm never dies.
I am _obviously_ talking about the prototype mechanism (notice the
quotes around "class" in the first post).

Gregor Kofler ha scritto:

sheldonlg meinte:

>Oops, I thought I was in a different newsgroup. I don't know about
classes in javascript.

No one knows.

Gregor

[CAFxX]

hmmm, I don't get what OldA.apply is supposed to be...

Joost Diepenmaat ha scritto:

CAFxX <us********@REMOVEMEcafxx.cjb.netwrites:

>I'm trying to solve a problem with my code but can't come up with a
solution.
Suppose I have a "class" A with its constructor (that I can't modify
directly)

function A() {
/* constructor code */
};
what I'd like to do is to make the constructor call a certain function
I specify before returning, i.e.

function A() {
/* constructor code */
someFunction();
};

is this possible?
CAFxX

You mean you want to replace the constructor A at runtime with some other
function that calls the original A and then adds some more
functionality?

var OldA = A;
A = function() {
OldA.apply(this,arguments);
// do new stuff here
};

// copy any properties set on OldA
for (p in OldA) {
if (OldA.hasOwnProperty(p)) {
A[p] = OldA[p];
}
// this may fix some potential issues
// and break some others
A.prototype.constructor = A;
}

If the original code tries hard enough, it can always detect that (and
break because) the constructor been replaced, and if there are already
instances of A around at the time the new constructor is created those
instances will be instanceOf OldA, not A.

see also:

http://joost.zeekat.nl/constructors-...confusing.html

HTH,
Joost.

[Joost Diepenmaat]

CAFxX <us********@REMOVEMEcafxx.cjb.netwrites:

hmmm, I don't get what OldA.apply is supposed to be...

somefunction.apply() calls the function passing a specific "this" and
arguments.

See, for example:

http://developer.mozilla.org/en/Core...Function/apply
--
Joost Diepenmaat | blog: http://joost.zeekat.nl/ | work: http://zeekat.nl/

[Gregor Kofler]

CAFxX meinte:

Right, sarcasm never dies.
I am _obviously_ talking about the prototype mechanism (notice the
quotes around "class" in the first post).

I noticed and I wasn't replying to you.

Gregor
--
http://photo.gregorkofler.at ::: Landschafts- und Reisefotografie
http://web.gregorkofler.com ::: meine JS-Spielwiese
http://www.image2d.com ::: Bildagentur für den alpinen Raum