Why (new RegExp) type is function not object

**RobG** · Dec 8 '07, 04:05 AM

Re: Why (new RegExp) type is function not object

EME wrote:

typeof new RegExp
----------------------------------------------------
Why (new RegExp) type is function not object
>
very thanks for you consulation

A function is an object. The ECMA spec section 11.4.3 says that the
typeof operator returns 'function' for objects that are functions[1],
and 'object' for objects that aren't functions.

Note that IE doesn't do that, it returns 'object' for functions.

1. It actually says "native and implements [[call]]", but it means
function. :-)

--
Rob
"We shall not cease from exploration, and the end of all our
exploring will be to arrive where we started and know the
place for the first time." -- T. S. Eliot

**AKS** · Dec 8 '07, 05:36 AM

Re: Why (new RegExp) type is function not object

On 8 ÄÅË, 06:33, EME <megaupload.sh. ..@gmail.comwro te:

typeof new RegExp
----------------------------------------------------
Why (new RegExp) type is function not object
>

Actually, only SpiderMonkey creates function, evaluating -new RegExp-
expression. It's more like extension of the engine since the
calculated object has no properties length and prototype.

**AKS** · Dec 8 '07, 05:36 AM

Re: Why (new RegExp) type is function not object

On 8 ÄÅË, 09:03, RobG <rg...@iinet.ne t.auwrote:

>
Note that IE doesn't do that, it returns 'object' for functions.
>

I hope you meant: "it returns 'object' for host functions".

**EME** · Dec 8 '07, 08:05 AM

Re: Why (new RegExp) type is function not object

for furthur more,i have detail test below:
typeof new RegExp //result 'function' in Firefox, 'object' in IE6
new RegExp instanceof Function //result false in Firefox

(new RegExp)() in Firefox is same as (new RegExp).exec()

**David Mark** · Dec 8 '07, 01:15 PM

Re: Why (new RegExp) type is function not object

On Dec 8, 12:30 am, AKS <aksus...@yande x.ruwrote:

On 8 ÄÅË, 09:03, RobG <rg...@iinet.ne t.auwrote:
>
>
>

Note that IE doesn't do that, it returns 'object' for functions.

>
I hope you meant: "it returns 'object' for host functions".

I would think so.

**Thomas 'PointedEars' Lahn** · Dec 8 '07, 02:05 PM

Re: Why (new RegExp) type is function not object

David Mark wrote:

On Dec 8, 2:55 am, EME <megaupload.sh. ..@gmail.comwro te:

>new RegExp instanceof Function //result false in Firefox

>
It isn't an instance of Function (it is an instance of RegExp.)

It isn't an instance of anything, as that would imply class-based inheritance.

PointedEars
--
realism: HTML 4.01 Strict
evangelism: XHTML 1.0 Strict
madness: XHTML 1.1 as application/xhtml+xml
-- Bjoern Hoehrmann

**David Mark** · Dec 8 '07, 02:05 PM

Re: Why (new RegExp) type is function not object

On Dec 8, 8:57 am, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:

David Mark wrote:

On Dec 8, 2:55 am, EME <megaupload.sh. ..@gmail.comwro te:

new RegExp instanceof Function //result false in Firefox

>

It isn't an instance of Function (it is an instance of RegExp.)

>
It isn't an instance of anything, as that would imply class-based inheritance.
>

You are kidding right? The operator quoted above that sentence should
explain why I used that terminology.

**Thomas 'PointedEars' Lahn** · Dec 8 '07, 02:25 PM

Re: Why (new RegExp) type is function not object

David Mark wrote:

On Dec 8, 8:57 am, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:

>David Mark wrote:

>>On Dec 8, 2:55 am, EME <megaupload.sh. ..@gmail.comwro te:
>>>new RegExp instanceof Function //result false in Firefox
>>It isn't an instance of Function (it is an instance of RegExp.)

>It isn't an instance of anything, as that would imply class-based inheritance.

>
You are kidding right?

I am not.

The operator quoted above that sentence should explain why I used that terminology.

The operator above was borrowed from Java, a programming language that
uses only class-based inheritance, to ease programming in JavaScript for
developers that a familiar with Java. However, `instanceof' is only a
name, not a hint regarding the underlying concept of the operation in
implementations of Edition 3 of the ECMAScript Language Specification.
It is therefore inappropriate to speak of objects as instances of their
constructors.

Inheritance and the prototype chain - JavaScript | MDN

http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide:Details_of_the_Object_Model#Summary_of_Differences

In programming, inheritance refers to passing down characteristics from a parent to a child so that a new piece of code can reuse and build upon the features of an existing one. JavaScript implements inheritance by using objects. Each object has an internal link to another object called its prototype. That prototype object has a prototype of its own, and so on until an object is reached with null as its prototype. By definition, null has no prototype and acts as the final link in this prototype chain. It is possible to mutate any member of the prototype chain or even swap out the prototype at runtime, so concepts like static dispatching do not exist in JavaScript.

PointedEars
--
var bugRiddenCrashP ronePieceOfJunk = (
navigator.userA gent.indexOf('M SIE 5') != -1
&& navigator.userA gent.indexOf('M ac') != -1
) // Plone, register_functi on.js:16

**David Mark** · Dec 8 '07, 03:15 PM

Re: Why (new RegExp) type is function not object

On Dec 8, 9:15 am, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:

David Mark wrote:

On Dec 8, 8:57 am, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:

David Mark wrote:
>On Dec 8, 2:55 am, EME <megaupload.sh. ..@gmail.comwro te:
>>new RegExp instanceof Function //result false in Firefox
>It isn't an instance of Function (it is an instance of RegExp.)
It isn't an instance of anything, as that would imply class-based inheritance.

>

You are kidding right?

>
I am not.

That was a rhetorical question. I know you are serious about being
pedantic.

>

The operator quoted above that sentence should explain why I used that terminology.

>
The operator above was borrowed from Java, a programming language that
uses only class-based inheritance, to ease programming in JavaScript for

No kidding.

developers that a familiar with Java. However, `instanceof' is only a
name, not a hint regarding the underlying concept of the operation in

I wasn't taking a hint from it.

implementations of Edition 3 of the ECMAScript Language Specification.
It is therefore inappropriate to speak of objects as instances of their
constructors.

Thanks for that.

**RobG** · Dec 8 '07, 03:15 PM

Re: Why (new RegExp) type is function not object

On Dec 9, 1:06 am, David Mark <dmark.cins...@ gmail.comwrote:

On Dec 8, 9:15 am, Thomas 'PointedEars' Lahn <PointedE...@we b.de>

[...]

It is therefore inappropriate to speak of objects as instances of their
constructors.

>
Thanks for that.

Maybe the instanceof operator should be "constructedby" ? :-)

--
Rob

**John G Harris** · Dec 8 '07, 09:55 PM

Re: Why (new RegExp) type is function not object

On Sat, 8 Dec 2007 at 14:57:13, in comp.lang.javas cript, Thomas
'PointedEars' Lahn wrote:

>David Mark wrote:

>On Dec 8, 2:55 am, EME <megaupload.sh. ..@gmail.comwro te:

>>new RegExp instanceof Function //result false in Firefox

>>
>It isn't an instance of Function (it is an instance of RegExp.)

>
>It isn't an instance of anything, as that would imply class-based inheritance.

Let's be really pedantic now. "An instance of RegExp" is just short for

"The object is a member of the class of all those objects that could
possibly be constructed by the function named RegExp".

Let's be differently pedantic now. Here is a quote from the ECMAScript
standard :

"RegExp instances inherit properties" ...

John
--
John Harris

**Richard Cornford** · Dec 12 '07, 05:55 PM

Re: Why (new RegExp) type is function not object

RobG wrote:

On Dec 9, 1:06 am, David Mark wrote:

>On Dec 8, 9:15 am, Thomas 'PointedEars' Lahn wrote:

[...]

>>It is therefore inappropriate to speak of objects as
>>instances of their constructors.

>>
>Thanks for that.

>
Maybe the instanceof operator should be "constructedby" ? :-)

The - instanceof - operator makes an assertion about the runtime
relationship between the objects on an object's prototype chain and the
object/value referred to by the - prototype - property of a function at
the moment of the operation. Because the - prototype - properties of
functions can be assigned values at any time the results of -
instanceof - do not necessarily represent anything beyond the outcome of
the pertinent algorithms.

As usual, if the 'Class' concept has been employed in javascript code
design, not violated at runtime, and no attempt has been made to extend
that concept across possible multiple frames (so there is only a single
instance of each 'constructor') then javascript's - instanceof - can be
employed as if it was broadly analogous to Java's - instanceof -.
Unfortunately the coincidence of names tends to give people familiar
with Java the false impression that the two operators are more related
than they actually are (and then they whinge when they find out that the
relationship in javascript is much more specific and concrete than the
conceptual relationship that is implied in Java).

Richard.

Why (new RegExp) type is function not object

Why (new RegExp) type is function not object

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