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From "Onno Scheffers (JIRA)" <...@tapestry.apache.org>
Subject [jira] Updated: (TAPESTRY-2364) YSlow Recommendation: Write Scripts at bottom of page
Date Tue, 07 Oct 2008 00:41:44 GMT

     [ https://issues.apache.org/jira/browse/TAPESTRY-2364?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Onno Scheffers updated TAPESTRY-2364:

    Attachment: TestFast.html

To be honest, I didn't know it worked like this either and it seems to differ per browser.
On Firefox 3 (OSX) the effect is pretty obvious, even if you include just one js-file at the
end of the file. On other browsers the problems start to show up only when more js-files are
added to the end of the file (like Tapestry does).

So some browsers are smarter and do immediately include cached resources, but even they have
to include the javascript files one after another, which still takes many seconds with big
libraries like Prototype and scipt.aculo.us.

Here's a test-case, using big images and external resources to make things more apparent,
tested in Firefox 3, Opera and Safari (OSX, Mac Pro 8-core). Opera is the fastest, Firefox
seems to be slowest.

- sayHello.js is a Javacript file that simply shows an alert-box when it gets executed. It
will be included in the two example pages.

- TestSlow.html is how Tapestry does it now. I added a couple of large images on the page
and included several external js-files to the end of the page. It is most visible on first
page-load (or after the cache is cleared). The Javascript isn't executed until most of the
resources are loaded or have started loading.

- TestFast.html includes a couple of js-files in the HEAD section. The page stays white a
little longer, but the alert-box is shown immediately and before the page renders. 

> YSlow Recommendation: Write Scripts at bottom of page
> -----------------------------------------------------
>                 Key: TAPESTRY-2364
>                 URL: https://issues.apache.org/jira/browse/TAPESTRY-2364
>             Project: Tapestry
>          Issue Type: Improvement
>          Components: tapestry-core
>            Reporter: Howard M. Lewis Ship
>            Assignee: Howard M. Lewis Ship
>            Priority: Minor
>             Fix For: 5.0.12
>         Attachments: sayHello.js, TestFast.html, TestSlow.html
> Tapestry is already doing a good job on this, by writing the dynamically generated <script>
block at the bottom of the page, but the external scripts should also be down there.
> http://developer.yahoo.com/performance/rules.html#js_bottom

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