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How are arguments a legit argument to Array.slice?

In the code sample below, how are arguments a legitimate
argument to Array.slice?
Function.protot ype.bind = function(){
var fn = this, args = Array.prototype .slice.call(arg uments), object =
args.shift();
return function(){
return fn.apply(object ,
args.concat(Arr ay.prototype.sl ice.call(argume nts)));
};
};
var myObject = {};
function myFunction(){
return this == myObject;
}

myFunction.bind (myObject)();
Aug 28 '08 #1
12 2074
lorlarz wrote
In the code sample below, how are arguments a legitimate
argument to Array.slice?

Function.protot ype.bind = function(){
var fn = this, args = Array.prototype .slice.call(arg uments),
object = args.shift();
return function(){
return fn.apply(object ,
args.concat(Arr ay.prototype.sl ice.call(argume nts)));
};
};
var myObject = {};
function myFunction(){
return this == myObject;
}

myFunction.bind (myObject)();
Code that is intended to be read by humans (so anything posted to Usenet
with the intention of its being examined by other participants in a
group) should be indented (using spaces in posts not tabs as tabs don't
receive uniform (or necessarily useful) handling in newsreader
software).

In the code above - arguments - is never an argument to Array.slice. All
occurrences of - arguments - as an argument are as an argument to -
Function.protot ype.call -.

Richard.

Aug 28 '08 #2
On Aug 29, 6:36*am, lorlarz <lorl...@gmail. comwrote:
In the code sample below, how are arguments a legitimate
*argument to Array.slice?

Function.protot ype.bind = function(){
var fn = this, args = Array.prototype .slice.call(arg uments), object =
args.shift();
return function(){
return fn.apply(object ,
args.concat(Arr ay.prototype.sl ice.call(argume nts)));};
Seems to me that:

return fn.apply(object , args);

is sufficient.
--
Rob

Aug 29 '08 #3
On Aug 28, 6:16*pm, "Richard Cornford" <Rich...@litote s.demon.co.uk>
wrote:
lorlarz wrote


In the code sample below, how are arguments a legitimate
argument to Array.slice?
Function.protot ype.bind = function(){
var fn = this, args = Array.prototype .slice.call(arg uments),
object = args.shift();
return function(){
return fn.apply(object ,
args.concat(Arr ay.prototype.sl ice.call(argume nts)));
};
};
var myObject = {};
function myFunction(){
return this == myObject;
}
myFunction.bind (myObject)();

Code that is intended to be read by humans (so anything posted to Usenet
with the intention of its being examined by other participants in a
group) should be indented (using spaces in posts not tabs as tabs don't
receive uniform (or necessarily useful) handling in newsreader
software).

In the code above - arguments - is never an argument to Array.slice. All
occurrences of - arguments - as an argument are as an argument to -
Function.protot ype.call -.

Richard.- Hide quoted text -

- Show quoted text -
This code is from a draft of a new JavaScript book
by a major expert. He is grabbing
the arguments property of the function and passing
it as an argument to Array.prototype .slice

The contents of the arguments property that the function
receives is just the object myObject, so there seems to be
nothing to slice.

I may have to ask the author himself; perhaps this
is a code error in the draft.
Aug 29 '08 #4
On Aug 28, 8:22*pm, RobG <rg...@iinet.ne t.auwrote:
On Aug 29, 6:36*am, lorlarz <lorl...@gmail. comwrote:
In the code sample below, how are arguments a legitimate
*argument to Array.slice?
Function.protot ype.bind = function(){
var fn = this, args = Array.prototype .slice.call(arg uments), object=
args.shift();
return function(){
return fn.apply(object ,
args.concat(Arr ay.prototype.sl ice.call(argume nts)));};

Seems to me that:

* return fn.apply(object , args);

is sufficient.

--
Rob
Yes, what you say at least makes sense to me.
Aug 29 '08 #5
lorlarz <lo*****@gmail. comwrites:
On Aug 29, 9:34*am, "Richard Cornford" <Rich...@litote s.demon.co.uk>
wrote:
>Richard.- Hide quoted text -

- Show quoted text -

You were automatically quoted by google and it looks correct to
me. There is just a single ">" in front of your lines and
">>" in front of where you quote me.
There is also the text "- Hide quoted text -" and "- Show quoted
text", which are attributed to Richard, and that wasn't there in his
message.
In any case, I simple took the google quote and did nothing
but reply below. If there is any validity to your
concern, you will have to take it up with google.
Uhm, no. You are responsible for the tools you chose to use.
If Google Groups doesn't work satisfactory, you should take
it up with Google.
I am trying, but do not yet quite understand your
explanation. Could you spell it out bit by bit
more?
I'm jumping into the middle here, but was the problem the
interpretation of
Array.prototype .slice.call(arg uments)

This calls the "call" method on the function "Array.prototyp e.slice"
with the argument "arguments" .

This gives approximatly the same effect as placing the function
as a method of the arguments object and calling it.

arguments.somen ame = Array.prototype .slice;
... arguments.somen ame();

just without actualy creating a property on the arguments object.

(As with my last reply, I used the google
quotinog of your post and did nothing
to alter the way it was quoted.)
And it again introduced spurious text. Maybe you will have
to do something to avoid this, since nothing apparently
doesn't do the job :)

--
Lasse Reichstein Nielsen
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'
Aug 29 '08 #6
lorlarz <lo*****@gmail. comwrites:

(you can trim your quotings a lot more without losing context)
Let me see if I can spell the situation out for myself.
The call method looks for a real array
No. The call method looks for an object and, optionally, some more
arguments.
and thus converts
the arguments object into a real array and then sends
the first argument of that resultant array
to the call method as the context
for "this" and IF there where any more arguments
(which in this example there are not), they would
be passed to the called function (Array.slice) IN
that context.
The call method the calls the "Array.prototyp e.slice" function with
"this" set to that object. I.e., when calling "slice", it is as if it
was a method on the arguments object.

The slice function is generic, and doesn't need an array as its "this"
value, just something with a "length" property.
The slice function then creates a new array that contains the same
elements as its "this" value. This converts the arguments object
to an array (or rather, creates a new array).
If this is correct, I guess my only remaining question
is what is the word "prototype" in this statement
var args = Array.prototype .slice.call(arg uments); ??
Array.prototype .slice references a function. This is the same function
that Array objects inherit through their prototype chain. I.e., if
var a = [];
is an array, then Array.prototype .slice and a.slice is the same function.

/L
--
Lasse Reichstein Nielsen
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'
Aug 29 '08 #7
RobG <rg***@iinet.ne t.auwrites:
On Aug 29, 6:36*am, lorlarz <lorl...@gmail. comwrote:
>In the code sample below, how are arguments a legitimate
*argument to Array.slice?

Function.proto type.bind = function(){
var fn = this, args = Array.prototype .slice.call(arg uments), object =
args.shift() ;
return function(){
return fn.apply(object ,
args.concat(Ar ray.prototype.s lice.call(argum ents)));};

Seems to me that:

return fn.apply(object , args);

is sufficient.
The above code allows partial application. I.e.,

function foo(a,b,c) { /*...*/ }
var foob = foo.bind(object , 42);
foob(37,"doh"); // equvialent to object.call(foo ,42,37,"doh")

The conversion from arguments-object to array is probably used because
the "concat" function requires an array as argument, and preferably an
array to work on (although it might work on an arguments object).

/L
--
Lasse Reichstein Nielsen
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'
Aug 29 '08 #8
On Aug 29, 2:40*pm, Lasse Reichstein Nielsen <lrn.unr...@gma il.com>
wrote:
I'm jumping into the middle here, but was the problem the
interpretation of
*Array.prototyp e.slice.call(ar guments)

This calls the "call" method on the function "Array.prototyp e.slice"
with the argument "arguments" .

This gives approximatly the same effect as placing the function
as a method of the arguments object and calling it.

*arguments.some name = Array.prototype .slice;
*... arguments.somen ame();

just without actualy creating a property on the arguments object.
[snip]
--
Lasse Reichstein Nielsen
*DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
* 'Faith without judgement merely degrades the spirit divine.'
Believe it or not, I think I understand. The function is
being called with only one argument (the arguments object)
and thus that is the context of the function call on
the slice method. Did I say that correctly?
Aug 29 '08 #9
On Aug 29, 2:48*pm, Lasse Reichstein Nielsen <lrn.unr...@gma il.com>
wrote:
[snip]
>
Array.prototype .slice references a function. This is the same function
that Array objects inherit through their prototype chain. I.e., if
*var a = [];
is an array, then Array.prototype .slice and a.slice is the same function.

/L
--
Lasse Reichstein Nielsen
*DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
* 'Faith without judgement merely degrades the spirit divine.'
Again, I believe I understand. If you are not
dealing with a specific array, you need to
call Array.prototype to use the slice method.

I am still not clear on why Array.slice would not
work though. Have an old Java background
that might be causing confusion.
Aug 29 '08 #10

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