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Differences in JS Load order IE7 vs. IE8
04-20-2010, 08:47 PM
Post: #1
Differences in JS Load order IE7 vs. IE8
Hi Pat!

I did today two tests of http://www.alice.de. One with IE7 and one with IE8. What I saw is a difference in the load order of Javascript Files.

In IE7 (here: http://www.webpagetest.org/result/100420_7PT1/)
you can see, that IE7 loads assets sequentially. The two JS files from the HEAD being loaded almost at the beginning.
Much later on, after some graphics, it loads further JS files from the BODY.

In IE8 (here: http://www.webpagetest.org/result/100420_7PSZ/)
you can see, that IE8 loads ALL of the JS files at the beginning. Ignoring, that most of them are referenced much later in the page, in the BODY.

(You can notify this also by the better grade for Combining JS.
Source for the site is identical for both Browsers. And Start Render is for IE7 quicker than for IE8)

Am I reading this correct? And why is IE8 doing this? Anyway to prevent IE8 from doing this?

Kind regards,
Markus
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04-20-2010, 09:20 PM
Post: #2
RE: Differences in JS Load order IE7 vs. IE8
Try doing multiple runs to see if the timing is consistent or if it was a fluke (not the order of load). IE8 will pre-fetch the javascript files but it will not block on them or execute the code until the appropriate time and it shouldn't interfere with the critical path to start render.
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04-20-2010, 11:06 PM
Post: #3
RE: Differences in JS Load order IE7 vs. IE8
(04-20-2010 09:20 PM)pmeenan Wrote:  Try doing multiple runs to see if the timing is consistent or if it was a fluke (not the order of load). IE8 will pre-fetch the javascript files but it will not block on them or execute the code until the appropriate time and it shouldn't interfere with the critical path to start render.

Actually I tested with HTTPWatch as well and saw the same pattern.

Also, if you look here http://www.webpagetest.org/result/100420...1/details/ at the connection view, you can clearly see, that no Non-JS Files will be fetched, up until the last JS file has been fully received. Most of the connections are idling, not fetching anything, due to the big JS file still being downloaded.
IE8 will load JS's in parallel, but no other asset.
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