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From "Ben Gidley (JIRA)" <j...@apache.org>
Subject [jira] Updated: (TAP5-769) JavaScript aggregation can be inefficient across multiple pages with different JS requirements
Date Fri, 17 Jul 2009 11:37:15 GMT

     [ https://issues.apache.org/jira/browse/TAP5-769?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Ben Gidley updated TAP5-769:

    Attachment: 0004-TAP-769.patch

Here is a patch that implements a solution for this. 

This changes the DocumentLinker and RenderSupportImpl so that scripts can be 'grouped' prior
to assembly into a single script.

The default behaviour now is to create one 'group' from the ClientInfrastructure stack and
a second group from everything else.

This should address a good percentage of this problem raised in this issue. 

Further enhancements that could be made
* Add method to render support to users to create their own groups
* Add a contribution point (similar to that provided by http://tapestry.formos.com/projects/ioko-tapestry-commons/tapestry-javascript/)
could be provided to allow inclusion of stacks on certain pages
* A further contribution to allow replacement for a stack rolled up javascript with a 'production'
one e.g. from a CDN. 

This patch does not address this issue of the length of the filename for the 'stack'. I can't
see an easy, generic and cluster safe way to implement that (except via the contribution mentioned

> JavaScript aggregation can be inefficient across multiple pages with different JS requirements
> ----------------------------------------------------------------------------------------------
>                 Key: TAP5-769
>                 URL: https://issues.apache.org/jira/browse/TAP5-769
>             Project: Tapestry 5
>          Issue Type: Bug
>          Components: tapestry-core
>    Affects Versions:
>            Reporter: Andy Blower
>         Attachments: 0002-TAP-769.patch, 0003-TAP-769.patch, 0004-TAP-769.patch
> I think Tapestry's JavaScript combination functionality is flawed. Each page & component
specifies which JS files it needs, which means that JS can be split into functional units
(good for development & maintenance) and only the JS that's actually needed for that page
is added for the client to download. The consequence of this is that pages can have lots of
JS files to download, all of which has to be downloaded before the page is loaded/rendered
now that the script link tags are enforced to be back in the head section. Our search results
page has 34 JS files for instance.
> Yahoo's YSlow tool recommends that these files are combined and minified, and Tapestry
includes functionality to do the first (minifying is on the TODO list I believe) probably
as a response to this recommendation which is good. Unfortunately the implementation based
on only having the JS files required for a page means that the combined JS can easily be unique
for most pages of a site. This means that the client browser has to download & cache lots
of large JS multiple times (prototype, scriptaculous, tapestry etc) as part of bigger combined
files, which I think is probably worse than requesting them separately, but only downloading
stuff once and using that for all pages.
> To solve this issue, Tapestry script combination could combine all of the scripts needed
for the site, and not just the unique set for each page. That way only a single JS file needs
to be downloaded and cached by the client browser. I'm aware that this may not be that easy
given the existing way only scripts needed for the page are put on it, so an alternative solution
that may be easier to implement would be to combine scripts into two files for each page.
The first file would contain all of the commonly Tapestry provided JS such as prototype.js,
scriptaculous.js, effects.js, tapestry.js, etc in one file that's the same for every page,
and have the rest in a second file that is unique for the page but that is not likely to include
very large JS files, just many little ones.
> A second flaw that the combination has is that if an external JS file is requested, script
combination is aborted rather than just excluding the external file from the combination.
> One other thing that surprised me about Tapestry's script combination is the length of
the generated filename, for example it's 919 characters long for a page on our site.

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