Reasons to not use a simple ondomload signal?
csnyder
I've been using the following trick successfully for a few months now.
It _seems_ to work fine cross-browser and cross platform.
<script type="text/javascript">
signal(window,'ondomload');
</script>
</body>
</html>
But based on the recent thread about implementing ondomload, I assume
that there must be cases when a simple signal at the end of the dom
isn't enough.
Can anyone give me a quick earful about why the above isn't the best
way to do it?
--
Chris Snyder
http://chxo.com/
machineghost
expert), the ordering is as follows:
1. Browser reads page line by line; every time it reads enough lines
to complete a JS statement, it executes that statement; meanwhile, non-
JS content is loaded in to the DOM as it is read
2. Once the browser has finished reading the page it will have a
complete DOM ... in memory.
3. The browser will then render that DOM tree to your screen.
4. Once it has finished rendering the DOM tree, it invokes any
"onload" events.
Technically that's wrong, because the first three things are really
happening simultaneously (ie. the browser starts rendering the top of
the page even before it has a complete DOM loaded), but it's simpler
to think of it that way (because they will almost always finish in
that order).
The "problem" with your code, as I understand it, is that your code
goes off in #1, which means there is no guarantee that a complete DOM
will exist. If you instead wait for "onLoad" though, you have to wait
for the page to render. So what people who are interested in the
"onDOMLoad" event are after is getting an event that triggers after 2
but before 3. That way, you don't have to wait for the page to
render, and as long as your code doesn't require any rendered
information (like "what are the dimensions of $('someElement')") it
should work fine.
But all of the above was written with my very flawed understanding of
the JS event model; please take it with a giant helping of salt.
Jeremy
Per Cederberg
interesting blog entry about page loading recently. It explains some
of the difficulties involved from a browser perspective:
http://webkit.org/blog/166/optimizing-page-loading-in-web-browser/
And a small extract of the most relevant section:
---
Problems start when a document contains references to external
scripts. Any script can call document.write(). Parsing can't proceed
before the script is fully loaded and executed and any
document.write() output has been inserted into the document text.
Since parsing is not proceeding while the script is being loaded no
further requests for other resources are made either. This quickly
leads to a situation where the script is the only resource loading and
connection parallelism does not get exploited at all. A series of
script tags essentially loads serially, hugely amplifying the effect
of latency.
---
So, in my understanding, putting a <script> tag at the very end of the
HTML text on the page should be nearly identical to actually waiting
for the onDOMLoad event. All the document text should have been parsed
already and be available in the DOM tree.
One of the many issues with "onload" is also the latency involved in
loading images and CSS files, which actually adds up to quite some
time (as most browsers only request 2 objects simultanously per web
site).
/Per
Bob Ippolito
is that you need to instrument all of your pages with that script tag
at the bottom. It's "nicer" to do it via DOM calls because you don't
need to change the markup.
-bob
Per Cederberg
of at least one other working implementation.
/Per
On Thu, May 8, 2008 at 11:02 PM, David Janes <david...@blogmatrix.com> wrote:
> And just to jump in here -- surely there's a "done" solution for this that
> we like, can we not just port something from another toolkit?
> Regards, etc...
> --
> David Janes
> Founder, BlogMatrix
> http://www.blogmatrix.com
> http://www.onaswarm.com
>
>
>