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Really good news. My vocabulary may to be too limited to tell you how great the latest changes in IE7 RC1 are. Microsoft announced that they have "recently made some great fixes to our engine to improve the garbage collection routine and to reduce unbounded memory growth." and that one "should see noticeable improvements on AJAX sites in the Release Candidate we shipped last week". Yes indeed, we do see tremendeous improvements. :-)

In fact many demos of qooxdoo run much faster now in IE7 compared to IE6. And they are even faster than in Firefox 1.5 in many cases. This is a huge jump in performance. Microsoft did not tell about their exact modifications, of course. Anyway, they have fixed the major problem of large JavaScript-based web applications. This problem, despite having a catchy name, was mentioned many times before like here, here and there: If you have many objects created, which are simply accessible in the current scope, all methods and features of JavaScript slow down dramatically. Yeah, right, the entire execution speed drops significantly. No other browser besides IE shows such a strange behavior. It is quite interesting that IE6 really gets slower the larger the total number of (accessible) objects. Sure, it is logical that more instanciated objects need more memory, but it is not logical that at the same time this will dramatically reduce the performance of any code (that is not even accessing this data).

With the release candidate RC1 of their new browser version IE7, it seems that they have finally fixed this issue. You can test it yourself in this test case, which has been available in qooxdoo for several months to analyze and measure the IE performance problems. Please look at status bar of your browser (maybe you need to enable the status bar in the IE7 security settings). It will display the execution time of each loop while a large number of objects exists. On my machine the IE6 needs ~1400ms, while IE7 needs ~30ms, which is roughly the time Firefox 1.5 needs. Definitely incredible! Bright future for modern web applications. :-)