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https://issues.apache.org/jira/browse/TAPESTRY-2364?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12637193#action_12637193
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Onno Scheffers commented on TAPESTRY-2364:
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> But the DOM isn't loaded any faster just because you put the script tag
> further up in your document, you still need to load the entire page first.
Well, the DOM is loaded faster if you put the scripts tags outside of the HEAD
tag, since the browsers waits until everything in the HEAD is loaded, while it
doesn't wait for resources outside of the head. So it does give a speedup if
you place the scripts at the bottom of the file.
> If I understand your concern, you want your user to see a blank page while
> waiting for scripts in <head> to load, rather than your user seeing the full
> page while waiting for scripts at the bottom of the page to load?
That's right. Usually css-files are placed in the HEAD to make sure they are
loaded before rendering. But often Javascript is used for toggling styles or
hiding things as well, so it should be possible to execute that Javascript
before the page is shown to the user.
> I believe that's the opposite of what most others want so it should probably
> not be the default behaviour.
I'm not sure I agree. If you look at any of the example pages of any of the
Javascript-frameworks. They pretty much all use a dom:loaded event to alter the
HTML before the page gets rendered and it's not just Prototype. It's also one
of the first items the JQuery tutorial teaches you for example:
http://docs.jquery.com/Tutorials:Getting_Started_with_jQuery#Hello_jQuery
> I believe putting scripts at the bottom so that the page renders faster is
> likely what most people want. If someone actually wants the page to render
> slower or needs to execute a script before the dom is loaded, there could be
> a simple workaround or a configuration option for putting scripts at the top
> of the page.
It is really quite common to have the Javascript in the HEAD section and
currently it is not possible in Tapestry. It should at least be configurable. I
still think it should be default behavior as well since you are forcing people
to change the configuration to do the most-common thing, while usually you'll
start configuring things only if you want to tweak the performance.
Also, the overhead of placing those files in the HEAD is minimal, since the
browser caches the js-files.
> 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
>
>
> 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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