Array and Hash (Associative array) in JavaScript v.3.0

[VK]

Whatever you wanted to know about it but always were affraid to ask.

<http://www.geocities.c om/schools_ring/ArrayAndHash.ht ml>

[Kevin Newman]

I'm so confused :-)

Douglas Crockford wrote:

The simple rule is this: If all of your indexes are non-negative
integers, use an array []. Otherwise, use an object {}.

This is what I originally thought, which is why I used an array. But I'm
using for...in to iterate my array.

Having thought about this, I think it might be best to use a standard
for loop since that will be more consistent with an array, and it would
allow me to only iterate integer indexes, so that if someone messes with
Array.prototype to add Array.push or something similar, it will not get
iterated like it would with for...in.

I'll just have to figure out how to keep the indexes contiguous when I
remove an element (I'm guessing there is a way to do that using
Array.slice, instead of delete - I'll have to experiment).

Thanks for all the info, it's been fun :-)

Kevin N.

[Michael Winter]

On 01/08/2005 17:31, Kevin Newman wrote:

[snip]

I'll just have to figure out how to keep the indexes contiguous when I
remove an element (I'm guessing there is a way to do that using
Array.slice, instead of delete - I'll have to experiment).

The Array.prototype .splice method[1] can be used to delete (and insert)
elements at arbitrary locations within an array. Essentially, it just
copies values about. However, this is a problem that I alluded to when I
mentioned the differences between sequential and linked data structures.
With the former, insertions and deletions at any location except the end
require all elements after the point of change to be shifted which, in a
large structure, can take a long time. With linked lists, it's simply a
matter of changing the links as the new element can be added anywhere in
memory (for insertion) or just forgotten about (for deletion).

Sequential structures offer fast, random look ups, but as yours will
always be complete iteration through the collection, this is only an
advantage when inserting or deletion at specific locations. Even then,
insertion for you will always be at the end once you've checked that the
new element is not a duplicate (more complete iteration). That just
leaves deletion, which should be rare anyway.

Despite how it may seem, I'm not necessarily pushing for you to use a
list. I do, but it's up to you to decide for yourself. Theoretical
reasons don't always in scripting, particularly as ECMAScript Arrays
don't have the same drawbacks that 'real' arrays do (including
reallocation during insertion).

Mike
[1] Not available in JScript 5 (usually IE5.0) and earlier.

--
Michael Winter
Prefix subject with [News] before replying by e-mail.

[Grant Wagner]

"Richard Cornford" <Ri*****@litote s.demon.co.uk> wrote in message
news:dc******** ***********@new s.demon.co.uk.. .

You are right. And Mozilla is wrong in not having the result of its
Array methods being as sparse and the original object. Though that
makes
it less reasonable of VK to assert that the array methods imply that
that arrays are continuous sequences of storage locations.

It also means that Mozilla browsers are open to 'malicious' actions
such
as:-

var a = [];
a[4294967294] = 'x';
a.reverse();

- being harmless to IE while having Mozilla grind to a halt, and
eventually cripple the entire OS.

Richard.

Not harmless in Internet Explorer 6.0.2900 here. CPU usage climbed to
90+% and stayed there for several minutes. jscript.dll version
5.6.0.8825

In Firefox 1.0.6, CPU rises to 90+% and stays there, eventually the
application generates an error and

Opera 8.02 returns almost immediately from a.reverse(), but attempting
to do -document.write( a);- results in a hung application.

--
Grant Wagner <gw*****@agrico reunited.com>
comp.lang.javas cript FAQ - http://jibbering.com/faq

[Lasse Reichstein Nielsen]

"Grant Wagner" <gw*****@agrico reunited.com> writes:

"Richard Cornford" <Ri*****@litote s.demon.co.uk> wrote in message
news:dc******** ***********@new s.demon.co.uk.. .

var a = [];
a[4294967294] = 'x';
a.reverse();

Opera 8.02 returns almost immediately from a.reverse(), but attempting
to do -document.write( a);- results in a hung application.

That's because the default string representation of that array would
be an "x" followed by 4294967294 commas. You asked for it, prepare to
wait :)

/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'

[Martin Honnen]

Lasse Reichstein Nielsen wrote:

Then Mozilla isn't ECMA 262 conforming, because ECMA262 v3 section
15.4.4.8 specifies the behavior of Array.prototype .reverse such that
the result should still be 2. Both Opera and IE gives 2.

The bug with reverse has been fixed recently in Mozilla so in a Mozilla
1.8 nightly or Deer Park nightly the result should be 2 too.
Here is the bug:
<https://bugzilla.mozill a.org/show_bug.cgi?id =299738>

--

Martin Honnen
http://JavaScript.FAQTs.com/

[Martin Honnen]

Lasse Reichstein Nielsen wrote:

Mozilla (in my case Firefox v1.04) have other array-related bugs,
e.g.,

var a = [0,,,,,,,,,,,,,, ,,,,,19];

also gives a count of 20 elements in Firefox, but 2 in IE, Opera and
the ECMA 262 standard.

This is filed as a bug but not fixed yet:
<https://bugzilla.mozill a.org/show_bug.cgi?id =260106>

--

Martin Honnen
http://JavaScript.FAQTs.com/