new foo.prototype.bar(x,y,z ) ?

[kj]

OK, here's another construct I've run into in the jQuery source
that I can't figure out. It looks like this:

return new jQuery.prototype.init( selector, context );

So basically, as far as I can tell, the returned value has the form

new obj.prototype.method( args );

(In addition, FWIW, the function jQuery.prototype.init has several
explict return statements which, as far as I can tell, all end up
returning "this".)

What I find most confusing here is that when I check the constructor
property of the newly created object I find that it is *not*
jQuery.prototype.init. I.e. the boolean expression

( new jQuery.prototype.init( selector, context ) ).constructor
=== jQuery.prototype.init

evaluates to *false*. Even if I test the value of this.constructor
at a breakpoint right at the top of jQuery.prototype.init, what I
get is Object, not jQuery.prototype.init. Contrast this behavior
with

function Foo () {
alert( this.constructor === Foo );
}
x = new Foo();

In this case the alert dialog will display "true", as one would
expect.

I've tried many different variants of this test and I have never
been able to replicate the situation in which the constructor
property of the this object in the scope of a function that has
been called using the new keyword is anything other than the function
in question. These tests included the case in which the function
explicitly returns the this object. (I even ran some of these
tests in SpiderMonkey running on Linux to rule out the possibility
that what I was seeing was either a Firebug artefact or a quirk in
the Firefox implementation of Javascript. I got the same results.)

This is utterly baffling to me...

If anyone can explain to me what's going on I'd appreciate it!

Thanks!

Kynn

 

[liamgegan]

OK, here's another construct I've run into in the jQuery source
that I can't figure out. It looks like this:

return new jQuery.prototype.init( selector, context );

So basically, as far as I can tell, the returned value has the form

new obj.prototype.method( args );

(In addition, FWIW, the function jQuery.prototype.init has several
explict return statements which, as far as I can tell, all end up
returning "this".)

What I find most confusing here is that when I check the constructor
property of the newly created object I find that it is *not*
jQuery.prototype.init. I.e. the boolean expression

( new jQuery.prototype.init( selector, context ) ).constructor
=== jQuery.prototype.init

evaluates to *false*. Even if I test the value of this.constructor
at a breakpoint right at the top of jQuery.prototype.init, what I
get is Object, not jQuery.prototype.init. Contrast this behavior
with

function Foo () {
alert( this.constructor === Foo );
}
x = new Foo();

In this case the alert dialog will display "true", as one would
expect.

I've tried many different variants of this test and I have never
been able to replicate the situation in which the constructor
property of the this object in the scope of a function that has
been called using the new keyword is anything other than the function
in question. These tests included the case in which the function
explicitly returns the this object. (I even ran some of these
tests in SpiderMonkey running on Linux to rule out the possibility
that what I was seeing was either a Firebug artefact or a quirk in
the Firefox implementation of Javascript. I got the same results.)

This is utterly baffling to me...

If anyone can explain to me what's going on I'd appreciate it!

Thanks!

Kynn

Try:
( new jQuery.prototype.init( selector, context ) ).constructor
== jQuery

and tell me what it says. Specifically, look for the following line of
code for a reference to the init constructors prototype:
jQuery.prototype.init.prototype = jQuery.prototype;

 

[kj]

Try:
( new jQuery.prototype.init( selector, context ) ).constructor
== jQuery

and tell me what it says.

Firebug at least reports that boolean expression as false.

Specifically, look for the following line of
code for a reference to the init constructors prototype:
jQuery.prototype.init.prototype = jQuery.prototype;

I see, but still, the constructor is not jQuery...

Kynn

 

[Joost Diepenmaat]

Firebug at least reports that boolean expression as false.


I see, but still, the constructor is not jQuery...

As I said in the previous thread, object.constructor is unreliable
unless the person writing the constructor method has taken care that it
works.

You usually don't need it to work anyway, since instanceof works
better.

Joost.

 

[kj]

As I said in the previous thread, object.constructor is unreliable
unless the person writing the constructor method has taken care that it
works.

You usually don't need it to work anyway, since instanceof works
better.

But there's one situation in which only constructor could help
(though it may not), and that is when one wants to find out the
class of an object. instanceof only helps one test against a
specific class, but what if one wanted to find out an objects class
in the first place?

kynn