How are arguments a legit argument to Array.slice?

Discussion in 'Javascript' started by lorlarz, Aug 28, 2008.

  1. lorlarz

    lorlarz Guest

    In the code sample below, how are arguments a legitimate
    argument to Array.slice?


    Function.prototype.bind = function(){
    var fn = this, args = Array.prototype.slice.call(arguments), object =
    args.shift();
    return function(){
    return fn.apply(object,
    args.concat(Array.prototype.slice.call(arguments)));
    };
    };
    var myObject = {};
    function myFunction(){
    return this == myObject;
    }

    myFunction.bind(myObject)();
    lorlarz, Aug 28, 2008
    #1
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  2. lorlarz wrote
    > In the code sample below, how are arguments a legitimate
    > argument to Array.slice?
    >
    > Function.prototype.bind = function(){
    > var fn = this, args = Array.prototype.slice.call(arguments),
    > object = args.shift();
    > return function(){
    > return fn.apply(object,
    > args.concat(Array.prototype.slice.call(arguments)));
    > };
    > };
    > 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.prototype.call -.

    Richard.
    Richard Cornford, Aug 29, 2008
    #2
    1. Advertising

  3. lorlarz

    RobG Guest

    On Aug 29, 6:36 am, lorlarz <> wrote:
    > In the code sample below, how are arguments a legitimate
    >  argument to Array.slice?
    >
    > Function.prototype.bind = function(){
    > var fn = this, args = Array.prototype.slice.call(arguments), object =
    > args.shift();
    > return function(){
    > return fn.apply(object,
    > args.concat(Array.prototype.slice.call(arguments)));};


    Seems to me that:

    return fn.apply(object, args);

    is sufficient.


    --
    Rob
    RobG, Aug 29, 2008
    #3
  4. lorlarz

    lorlarz Guest

    On Aug 28, 6:16 pm, "Richard Cornford" <>
    wrote:
    > lorlarz wrote
    >
    >
    >
    >
    >
    > > In the code sample below, how are arguments a legitimate
    > > argument to Array.slice?

    >
    > > Function.prototype.bind = function(){
    > > var fn = this, args = Array.prototype.slice.call(arguments),
    > > object = args.shift();
    > > return function(){
    > > return fn.apply(object,
    > > args.concat(Array.prototype.slice.call(arguments)));
    > > };
    > > };
    > > 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.prototype.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.
    lorlarz, Aug 29, 2008
    #4
  5. lorlarz

    lorlarz Guest

    On Aug 28, 8:22 pm, RobG <> wrote:
    > On Aug 29, 6:36 am, lorlarz <> wrote:
    >
    > > In the code sample below, how are arguments a legitimate
    > >  argument to Array.slice?

    >
    > > Function.prototype.bind = function(){
    > > var fn = this, args = Array.prototype.slice.call(arguments), object=
    > > args.shift();
    > > return function(){
    > > return fn.apply(object,
    > > args.concat(Array.prototype.slice.call(arguments)));};

    >
    > Seems to me that:
    >
    >   return fn.apply(object, args);
    >
    > is sufficient.
    >
    > --
    > Rob


    Yes, what you say at least makes sense to me.
    lorlarz, Aug 29, 2008
    #5
  6. lorlarz wrote:
    >On Aug 28, 6:16 pm, Richard Cornford wrote:
    >> lorlarz wrote

    ><snip>
    >>> In the code sample below, how are arguments a legitimate
    >>> argument to Array.slice?

    >>
    >>> Function.prototype.bind = function(){
    >>> var fn = this, args = Array.prototype.slice.call(arguments),
    >>> object = args.shift();
    >>> return function(){
    >>> return fn.apply(object,
    >>> args.concat(Array.prototype.slice.call(arguments)));
    >>> };
    >>> };
    >>> var myObject = {};
    >>> function myFunction(){
    >>> return this == myObject;
    >>> }

    >>
    >>> myFunction.bind(myObject)();

    >>
    >> Code that is intended to be read by humans ...
    >> should be indented ...

    ><snip>
    >> 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.prototype.call -.
    >>
    >> Richard.- Hide quoted text -

    ^^^^^^^^^^^^^^^^^^^^
    >> - Show quoted text -

    ^^^^^^^^^^^^^^^^^^^^^

    I did _not_ write that final text. Why are you attributing words to me
    that I did not write? That represents a serious breach of netiquette,
    and is disingenuous at the very least.

    > This code is from a draft of a new JavaScript book


    And the code is indented in that presentation (that is not a question,
    and I don't need to see it in order to *know* that it *is* indented).

    > by a major expert.


    YMMV

    > He is grabbing


    What it the technical meaning of "grabbing" in javascript?

    > the arguments property of the function and passing
    > it as an argument to Array.prototype.slice


    No he is not. That is not what the code above does, as I have already
    told you once; at no point in the code above does an - arguments -
    object get used as an argument to the - slice - method.

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


    The - slice - method is used in order to transfer the values of the
    'array index' properties of an - arguments - object to corresponding
    properties of a newly created Array object. This allows - shift - to be
    called on that Array in order to extract its first element (the
    reference to the - myObject - object) and leave any other values for
    later use in any call to the - fn - function.

    > I may have to ask the author himself;


    You still may have to work out what the correct question is.

    > perhaps this is a code error in the draft.


    No, the code is fine; a straight reproduction of a run-of-the-mill -
    bind - implementation. Obviously the accompanying text is not very
    effective as an explanation of what it going on here, but that is 'major
    experts' for you.

    Richard.
    Richard Cornford, Aug 29, 2008
    #6
  7. lorlarz

    lorlarz Guest

    On Aug 29, 9:34 am, "Richard Cornford" <>
    wrote:
    > lorlarz wrote:
    > >On Aug 28, 6:16 pm, Richard Cornford wrote:
    > >> lorlarz wrote

    > ><snip>
    > >>> In the code sample below, how are arguments a legitimate
    > >>> argument to Array.slice?

    >
    > >>> Function.prototype.bind = function(){
    > >>> var fn = this, args = Array.prototype.slice.call(arguments),
    > >>> object = args.shift();
    > >>> return function(){
    > >>> return fn.apply(object,
    > >>> args.concat(Array.prototype.slice.call(arguments)));
    > >>> };
    > >>> };
    > >>> var myObject = {};
    > >>> function myFunction(){
    > >>> return this == myObject;
    > >>> }

    >
    > >>> myFunction.bind(myObject)();

    >
    > >> Code that is intended to be read by humans ...
    > >> should be indented ...

    > ><snip>
    > >> 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.prototype.call -.

    >
    > >> Richard.- Hide quoted text -

    >
    >            ^^^^^^^^^^^^^^^^^^^^>> - Show quoted text -
    >
    >    ^^^^^^^^^^^^^^^^^^^^^
    >
    > I did _not_ write that final text. Why are you attributing words to me
    > that I did not write? That represents a serious breach of netiquette,
    > and is disingenuous at the very least.
    >
    > > This code is from a draft of a new JavaScript book

    >
    > And the code is indented in that presentation (that is not a question,
    > and I don't need to see it in order to *know* that it *is* indented).
    >
    > > by a major expert.

    >
    > YMMV
    >
    > > He is grabbing

    >
    > What it the technical meaning of "grabbing" in javascript?
    >
    > > the arguments property of the function and passing
    > > it as an argument to Array.prototype.slice

    >
    > No he is not. That is not what the code above does, as I have already
    > told you once; at no point in the code above does an - arguments -
    > object get used as an argument to the - slice - method.
    >
    > > The contents of the arguments property that the function
    > > receives is just the object myObject, so there seems to be
    > > nothing to slice.

    >
    > The - slice - method is used in order to transfer the values of the
    > 'array index' properties of an - arguments - object to corresponding
    > properties of a newly created Array object. This allows - shift - to be
    > called on that Array in order to extract its first element (the
    > reference to the - myObject - object) and leave any other values for
    > later use in any call to the - fn - function.
    >
    > > I may have to ask the author himself;

    >
    > You still may have to work out what the correct question is.
    >
    > > perhaps this is a code error in the draft.

    >
    > No, the code is fine; a straight reproduction of a run-of-the-mill -
    > bind - implementation. Obviously the accompanying text is not very
    > effective as an explanation of what it going on here, but that is 'major
    > experts' for you.
    >
    > 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.

    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.

    I am trying, but do not yet quite understand your
    explanation. Could you spell it out bit by bit
    more?

    I agree with you that the expert did indeed
    fail to explain the code, becuase he provides
    no explanation. You may have done a bit better,
    but I am still unclear. I think you may be able
    to bring me "over the line" if you just detail
    a bit more what happens.

    (As with my last reply, I used the google
    quotinog of your post and did nothing
    to alter the way it was quoted.)
    lorlarz, Aug 29, 2008
    #7
  8. lorlarz

    lorlarz Guest

    On Aug 29, 10:25 am, lorlarz <> wrote:
    > On Aug 29, 9:34 am, "Richard Cornford" <>
    > wrote:
    >
    >
    >
    >
    >
    > > lorlarz wrote:
    > > >On Aug 28, 6:16 pm, Richard Cornford wrote:
    > > >> lorlarz wrote
    > > ><snip>
    > > >>> In the code sample below, how are arguments a legitimate
    > > >>> argument to Array.slice?

    >
    > > >>> Function.prototype.bind = function(){
    > > >>> var fn = this, args = Array.prototype.slice.call(arguments),
    > > >>> object = args.shift();
    > > >>> return function(){
    > > >>> return fn.apply(object,
    > > >>> args.concat(Array.prototype.slice.call(arguments)));
    > > >>> };
    > > >>> };
    > > >>> var myObject = {};
    > > >>> function myFunction(){
    > > >>> return this == myObject;
    > > >>> }

    >
    > > >>> myFunction.bind(myObject)();

    >
    > > >> Code that is intended to be read by humans ...
    > > >> should be indented ...
    > > ><snip>
    > > >> 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.prototype.call -.

    >
    > > >> Richard.- Hide quoted text -

    >
    > >            ^^^^^^^^^^^^^^^^^^^^>> - Show quoted text -

    >
    > >    ^^^^^^^^^^^^^^^^^^^^^

    >
    > > I did _not_ write that final text. Why are you attributing words to me
    > > that I did not write? That represents a serious breach of netiquette,
    > > and is disingenuous at the very least.

    >
    > > > This code is from a draft of a new JavaScript book

    >
    > > And the code is indented in that presentation (that is not a question,
    > > and I don't need to see it in order to *know* that it *is* indented).

    >
    > > > by a major expert.

    >
    > > YMMV

    >
    > > > He is grabbing

    >
    > > What it the technical meaning of "grabbing" in javascript?

    >
    > > > the arguments property of the function and passing
    > > > it as an argument to Array.prototype.slice

    >
    > > No he is not. That is not what the code above does, as I have already
    > > told you once; at no point in the code above does an - arguments -
    > > object get used as an argument to the - slice - method.

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

    >
    > > The - slice - method is used in order to transfer the values of the
    > > 'array index' properties of an - arguments - object to corresponding
    > > properties of a newly created Array object. This allows - shift - to be
    > > called on that Array in order to extract its first element (the
    > > reference to the - myObject - object) and leave any other values for
    > > later use in any call to the - fn - function.

    >
    > > > I may have to ask the author himself;

    >
    > > You still may have to work out what the correct question is.

    >
    > > > perhaps this is a code error in the draft.

    >
    > > No, the code is fine; a straight reproduction of a run-of-the-mill -
    > > bind - implementation. Obviously the accompanying text is not very
    > > effective as an explanation of what it going on here, but that is 'major
    > > experts' for you.

    >
    > > 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.
    >
    > 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.
    >
    > I am trying, but do not yet quite understand your
    > explanation.  Could you spell it out bit by bit
    > more?
    >
    > I agree with you that the expert did indeed
    > fail to explain the code, becuase he provides
    > no explanation.  You may have done a bit better,
    > but I am still unclear.  I think you may be able
    > to bring me "over the line" if you just detail
    > a bit more what happens.
    >
    > (As with my last reply, I used the google
    >  quotinog of your post and did nothing
    >  to alter the way it was quoted.)- Hide quoted text -
    >
    > - Show quoted text -


    P.S. I do see what google is doing to you, Cornford,
    and it just did it to me ABOVE. I will make sure
    I make up for the terrible thing google does
    ALTHOUGH THAT "quoted text" IS ABSOLUTELY EMPTY
    and only a weird person would worry or take offense.

    No offense.

    Still, again, Cornford, I would be most appreciative
    if you could detail you last response (if possible).
    lorlarz, Aug 29, 2008
    #8
  9. lorlarz

    lorlarz Guest

    On Aug 29, 9:34 am, "Richard Cornford" <>
    wrote:
    > lorlarz wrote:
    > >On Aug 28, 6:16 pm, Richard Cornford wrote:
    > >> lorlarz wrote

    > ><snip>
    > >>> In the code sample below, how are arguments a legitimate
    > >>> argument to Array.slice?

    >
    > >>> Function.prototype.bind = function(){
    > >>> var fn = this, args = Array.prototype.slice.call(arguments),
    > >>> object = args.shift();
    > >>> return function(){
    > >>> return fn.apply(object,
    > >>> args.concat(Array.prototype.slice.call(arguments)));
    > >>> };
    > >>> };
    > >>> var myObject = {};
    > >>> function myFunction(){
    > >>> return this == myObject;
    > >>> }

    >
    > >>> myFunction.bind(myObject)();

    >
    > >> Code that is intended to be read by humans ...
    > >> should be indented ...

    > ><snip>
    > >> 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.prototype.call -.

    >
    > >> Richard.- Hide quoted text -

    >
    >            ^^^^^^^^^^^^^^^^^^^^>> - Show quoted text -
    >
    >    ^^^^^^^^^^^^^^^^^^^^^
    >
    > I did _not_ write that final text. Why are you attributing words to me
    > that I did not write? That represents a serious breach of netiquette,
    > and is disingenuous at the very least.
    >
    > > This code is from a draft of a new JavaScript book

    >
    > And the code is indented in that presentation (that is not a question,
    > and I don't need to see it in order to *know* that it *is* indented).
    >
    > > by a major expert.

    >
    > YMMV
    >
    > > He is grabbing

    >
    > What it the technical meaning of "grabbing" in javascript?
    >
    > > the arguments property of the function and passing
    > > it as an argument to Array.prototype.slice

    >
    > No he is not. That is not what the code above does, as I have already
    > told you once; at no point in the code above does an - arguments -
    > object get used as an argument to the - slice - method.
    >
    > > The contents of the arguments property that the function
    > > receives is just the object myObject, so there seems to be
    > > nothing to slice.

    >
    > The - slice - method is used in order to transfer the values of the
    > 'array index' properties of an - arguments - object to corresponding
    > properties of a newly created Array object. This allows - shift - to be
    > called on that Array in order to extract its first element (the
    > reference to the - myObject - object) and leave any other values for
    > later use in any call to the - fn - function.
    >
    > > I may have to ask the author himself;

    >
    > You still may have to work out what the correct question is.
    >
    > > perhaps this is a code error in the draft.

    >
    > No, the code is fine; a straight reproduction of a run-of-the-mill -
    > bind - implementation. Obviously the accompanying text is not very
    > effective as an explanation of what it going on here, but that is 'major
    > experts' for you.
    >
    > Richard.


    Let me see if I can spell the situation out for myself.
    The call method looks for a real array 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.

    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(arguments); ??

    I am doing all I can for myself. Can you
    bring me "over the line" , Richard??
    lorlarz, Aug 29, 2008
    #9
  10. lorlarz <> writes:

    > On Aug 29, 9:34 am, "Richard Cornford" <>
    > 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(arguments)

    This calls the "call" method on the function "Array.prototype.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.somename = Array.prototype.slice;
    ... arguments.somename();

    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/rasterTriangleDOM.html>
    'Faith without judgement merely degrades the spirit divine.'
    Lasse Reichstein Nielsen, Aug 29, 2008
    #10
  11. lorlarz <> writes:

    (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.prototype.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(arguments); ??


    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/rasterTriangleDOM.html>
    'Faith without judgement merely degrades the spirit divine.'
    Lasse Reichstein Nielsen, Aug 29, 2008
    #11
  12. RobG <> writes:

    > On Aug 29, 6:36 am, lorlarz <> wrote:
    >> In the code sample below, how are arguments a legitimate
    >>  argument to Array.slice?
    >>
    >> Function.prototype.bind = function(){
    >> var fn = this, args = Array.prototype.slice.call(arguments), object =
    >> args.shift();
    >> return function(){
    >> return fn.apply(object,
    >> args.concat(Array.prototype.slice.call(arguments)));};

    >
    > 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/rasterTriangleDOM.html>
    'Faith without judgement merely degrades the spirit divine.'
    Lasse Reichstein Nielsen, Aug 29, 2008
    #12
  13. lorlarz

    lorlarz Guest

    On Aug 29, 2:40 pm, Lasse Reichstein Nielsen <>
    wrote:

    > I'm jumping into the middle here, but was the problem the
    > interpretation of
    >  Array.prototype.slice.call(arguments)
    >
    > This calls the "call" method on the function "Array.prototype.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.somename = Array.prototype.slice;
    >  ... arguments.somename();
    >
    > just without actualy creating a property on the arguments object.
    >

    [snip]
    > --
    > Lasse Reichstein Nielsen
    >  DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleDOM.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?
    lorlarz, Aug 29, 2008
    #13
  14. lorlarz

    lorlarz Guest

    On Aug 29, 2:48 pm, Lasse Reichstein Nielsen <>
    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/rasterTriangleDOM.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.
    lorlarz, Aug 29, 2008
    #14
  15. lorlarz

    lorlarz Guest

    On Aug 29, 3:01 pm, Lasse Reichstein Nielsen <>
    wrote:
    > RobG <> writes:
    > > On Aug 29, 6:36 am, lorlarz <> wrote:
    > >> In the code sample below, how are arguments a legitimate
    > >>  argument to Array.slice?

    >
    > >> Function.prototype.bind = function(){
    > >> var fn = this, args = Array.prototype.slice.call(arguments), object =
    > >> args.shift();
    > >> return function(){
    > >> return fn.apply(object,
    > >> args.concat(Array.prototype.slice.call(arguments)));};

    >
    > > 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/rasterTriangleDOM.html>
    >   'Faith without judgement merely degrades the spirit divine.'- Hide quoted text -


    Indeed partial application is exactly the context the
    code came up in. I bow to your expertise. You certainly
    know what you are talking about. You surely
    have my respect.

    I will strive to make up for google's short-comings
    in responding to other. Best wishes.
    lorlarz, Aug 29, 2008
    #15
  16. lorlarz

    dhtml Guest

    lorlarz wrote:
    > On Aug 28, 6:16 pm, "Richard Cornford" <>
    > wrote:
    >> lorlarz wrote
    >>
    >>
    >>
    >>
    >>
    >>> In the code sample below, how are arguments a legitimate
    >>> argument to Array.slice?


    [snip]

    >
    > This code is from a draft of a new JavaScript book
    > by a major expert.


    LOL. I think I know whose book this is.

    He is grabbing
    > the arguments property of the function and passing
    > it as an argument to Array.prototype.slice
    >


    Is he using his sword?

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

    I think I see Lasse is helping you just a little too much. I've
    mentioned the EcmaScript specification to you before. Do a little
    research there first. You can search that specification for "call(" .
    Then search for "slice(" and see what that does.

    You can find the "unofficial edition" spec in HTML on bclary.com and the
    official version in pdf here:
    http://www.ecma-international.org/publications/standards/Ecma-262.htm

    Garrett
    dhtml, Aug 29, 2008
    #16
  17. lorlarz

    lorlarz Guest

    On Aug 29, 5:48 pm, dhtml <> wrote:
    > lorlarz wrote:
    > > On Aug 28, 6:16 pm, "Richard Cornford" <>
    > > wrote:
    > >> lorlarz wrote

    >
    > >>> In the code sample below, how are arguments a legitimate
    > >>> argument to Array.slice?

    >
    > [snip]
    >
    >
    >
    > > This code is from a draft of a new JavaScript book
    > > by a major expert.  

    >
    > LOL. I think I know whose book this is.
    >
    > He is grabbing
    >
    > > the arguments property of the function and passing
    > > it as an argument to Array.prototype.slice

    >
    > Is he using his sword?
    >
    > > The contents of the arguments property that the function
    > > receives is just the object myObject, so there seems to be
    > > nothing to slice.

    >
    > I think I see Lasse is helping you just a little too much.  I've
    > mentioned the EcmaScript specification to you before. Do a little
    > research there first. You can search that specification for "call(" .
    > Then search for "slice(" and see what that does.
    >
    > You can find the "unofficial edition" spec in HTML on bclary.com and the
    > official version in pdf here:http://www.ecma-international.org/publications/standards/Ecma-262.htm
    >
    > Garrett


    I really do not consider you to have a legitimate criticism
    of me asking the question. IF THIS rather hard-to-understand
    routine is not something one can ask about here, WHAT IS??
    One can _always_ find _all_ the answers elsewhere (FACT), but
    can sometimes learn more more clearly from some of the better
    people HERE. And, that is what the group is about. (Otherwise,
    if someone can always find the answer elsewhere & in _your view_
    should not ask the question here, NO QUESTIONS would be
    "legitimate" here!!!! Isn't this silly???)

    Now, how is this particular thing is harder than just call and
    slice? Well, first you must know that arguments is an object
    and that an object is seen as a single entity. Then you must
    realize that the first argument to call simply sets the
    context of "this" plus that slice is just being using to make
    this object a one element array. This is not something all
    readily understand.

    Truth is I have a remaining question . It is that in
    the code,
    return fn.apply(object,
    args.concat(Array.prototype.slice.call(arguments)));
    ,
    it seems apply (there) is potentially getting an extra,
    array element (because the first element in arguments
    is still the object (the one setting the context of "this).

    Thus, I am not sure I still fully understand and
    am trying not to be embarrassed asking the question
    HERE, despite criticism of asking the question I
    aready have.

    So, Lasse, I am still listening.
    lorlarz, Aug 31, 2008
    #17
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