Differences in JS Load order IE7 vs. IE8

Web Performance Discuss Test Results
1

Hi Pat!

I did today two tests of 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

2

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.

3

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

Also, if you look here WebPageTest Test - WebPageTest 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.