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Wierd use of "new function() {}"

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  Wierd use of "new function() {}" "Robert Crandal" <noreply2me@yahoo.com> - 2013-12-28 20:06 -0700
    Re: Wierd use of "new function() {}" "Robert Crandal" <noreply2me@yahoo.com> - 2013-12-28 20:42 -0700
      Re: Wierd use of "new function() {}" Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-12-29 17:45 +0100
    Re: Wierd use of "new function() {}" Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2013-12-29 02:26 -0200
      Re: Wierd use of "new function() {}" John Harris <niam@jghnorth.org.uk.invalid> - 2013-12-29 11:07 +0000
        Re: Wierd use of "new function() {}" Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2013-12-29 11:52 -0200
        Re: Wierd use of "new function() {}" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-12-29 19:39 +0000
          Re: Wierd use of "new function() {}" John Harris <niam@jghnorth.org.uk.invalid> - 2013-12-30 15:27 +0000

#22467 — Wierd use of "new function() {}"

Another question about John Resig's book, "Pro
JavaScript Techniques" (C) 2006.

On page 210, the following JavaScript code is
seen:

   for (i = 0; i < elem.length; i++) new function() {

          /* code snipped here */
   }

I don't think I've ever seen a "new function()" statement
used right after a "for" statement.  Is this valid code that
is used for a certain purpose?  Or am I looking at
another possible typo in the book?

Robert

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#22468

In case anyone wants to see the actual code, here it is:

//
// This code is supposed to initialize a slideshow over a
// particular image gallery.
//
function startShow(obj) {

  var elem = tag("li", obj);    // Locate elements by tag
  var gallery = id("gallery");  // Locate tag by ID

  for (var i = 0; i < elem.length; i++) new function() {
    var cur = elem[i];
    setTimeout(function() {
        showImage(cur);
        setTimeout(function() {
           fadeOut(gallery, 0, 10);
         }, 3500);
    }, i * 5000);
  }
  setTimeout(hideOverlay, 5000 * elem.length);
  showOverlay();
}

I was just confused about the use of the "new function() {}" as
seen above.  Hopefully someone can explain that to me.
Thanks!

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#22475

Robert Crandal wrote:

> In case anyone wants to see the actual code, here it is:
> 
> //
> // This code is supposed to initialize a slideshow over a
> // particular image gallery.
> //
> function startShow(obj) {
> 
>   var elem = tag("li", obj);    // Locate elements by tag
>   var gallery = id("gallery");  // Locate tag by ID
> 
>   for (var i = 0; i < elem.length; i++) new function() {
>     var cur = elem[i];
>     setTimeout(function() {
>         showImage(cur);
>         setTimeout(function() {
>            fadeOut(gallery, 0, 10);
>          }, 3500);
>     }, i * 5000);
>   }
>   setTimeout(hideOverlay, 5000 * elem.length);
>   showOverlay();
> }
> 
> I was just confused about the use of the "new function() {}" as
> seen above.  Hopefully someone can explain that to me.

It is the result of the common misconception that it would be necessary to 
call a function as a *constructor* in order to create a private scope.  
Evidently it does not make sense to call this function as a constructor; it 
does not even use “this”.

It is better written as follows:

  function startShow (obj)
  { 
    /* Locate elements by tag _name_ */
    var elem = tag("li", obj);

    /* Locate _element_ by ID */
    var gallery = id("gallery");
 
    for (var i = 0, len = elem.length; i < len; ++i)
    {
      (function (i) {
        var cur = elem[i];
        window.setTimeout(function () {
          showImage(cur);
          window.setTimeout(function () {
            fadeOut(gallery, 0, 10);
          }, 3500);
        }, i * 5000);
      }(i));
    }

    window.setTimeout(hideOverlay, 5000 * elem.length);
    showOverlay();
  }

Although these book reviews can be educational, it would take a lifetime 
explaining and correcting all of Resig's misconceptions.  I have better 
things to do, and so should you.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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#22469

On 29/12/2013 01:06, Robert Crandal wrote:
> Another question about John Resig's book, "Pro
> JavaScript Techniques" (C) 2006.
>
> On page 210, the following JavaScript code is
> seen:
>
>     for (i = 0; i < elem.length; i++) new function() {
>
>            /* code snipped here */
>     }
>
> I don't think I've ever seen a "new function()" statement
> used right after a "for" statement.  Is this valid code that
> is used for a certain purpose?  Or am I looking at
> another possible typo in the book?
>

new function () { } is a "constructor anonymous function", that creates 
a new Object {}.

Douglas Crockford once wrote: "It is never a good idea to put new 
directly in front of function. For example, new function provides no 
advantage in constructing new objects."
<http://yuiblog.com/blog/2006/11/13/javascript-we-hardly-new-ya/>

Coming from a John Resig's book, we can expect everything (the good, the 
bad and ugly).

-- 
Joao Rodrigues

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#22471

On Sun, 29 Dec 2013 02:26:02 -0200, Joao Rodrigues
<groups_jr-1@yahoo.com.br> wrote:


  <snip>
>Douglas Crockford once wrote: "It is never a good idea to put new 
>directly in front of function. For example, new function provides no 
>advantage in constructing new objects."
  <snip>

There's another dodgy author. What you've quoted may mislead people :
"new objects" should be "new function objects". There are advantages
when constructing other kinds of object.

  John 

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#22473

On 29/12/2013 09:07, John Harris wrote:
> On Sun, 29 Dec 2013 02:26:02 -0200, Joao Rodrigues
> wrote:
>
>
>    <snip>
>> Douglas Crockford once wrote: "It is never a good idea to put new
>> directly in front of function. For example, new function provides no
>> advantage in constructing new objects."
>    <snip>
>
> There's another dodgy author.

If you compare JavaScript books' authors, I think that Douglas Crockford 
is not so bad.

> What you've quoted may mislead people :
> "new objects" should be "new function objects". There are advantages
> when constructing other kinds of object.
>

Yes, what I've quoted may mislead people if they don't read the article 
containing Crockford's explanation:

<http://yuiblog.com/blog/2006/11/13/javascript-we-hardly-new-ya/>

But don't think that I'm one of his fanboys (if there are any). I don't 
like when Douglas rants against the equal operator (==) as if coercion 
was something to be avoided. Coercion is everywhere in JavaScript.

-- 
Joao Rodrigues

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#22481

John Harris <niam@jghnorth.org.uk.invalid> writes:

> On Sun, 29 Dec 2013 02:26:02 -0200, Joao Rodrigues
> <groups_jr-1@yahoo.com.br> wrote:
>
>   <snip>
>>Douglas Crockford once wrote: "It is never a good idea to put new 
>>directly in front of function. For example, new function provides no 
>>advantage in constructing new objects."
>   <snip>
>
> There's another dodgy author. What you've quoted may mislead people :
> "new objects" should be "new function objects". There are advantages
> when constructing other kinds of object.

That would not fit.  He is specifically talking about using "new
function" to create objects that are *not* functions.

-- 
Ben.

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#22490

On Sun, 29 Dec 2013 19:39:11 +0000, Ben Bacarisse
<ben.usenet@bsb.me.uk> wrote:

>John Harris <niam@jghnorth.org.uk.invalid> writes:
>
>> On Sun, 29 Dec 2013 02:26:02 -0200, Joao Rodrigues
>> <groups_jr-1@yahoo.com.br> wrote:
>>
>>   <snip>
>>>Douglas Crockford once wrote: "It is never a good idea to put new 
>>>directly in front of function. For example, new function provides no 
>>>advantage in constructing new objects."
>>   <snip>
>>
>> There's another dodgy author. What you've quoted may mislead people :
>> "new objects" should be "new function objects". There are advantages
>> when constructing other kinds of object.
>
>That would not fit.  He is specifically talking about using "new
>function" to create objects that are *not* functions.

Ah yes. I misread "new function" as "new Function". However, he still
fails to describe the advantage of using "new".

  John

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