IE7 class selector much slower after 1.8.0 release

[morrijr]

We upgraded our corporate website from 1.7.2 to 1.8.1 and immediately started taking calls on how much slower this release was, unfortunately, despite a major push from us we have been unable to get the majority of our customers off IE7 (something like 71%).

Please note that this is with regards to IE7 only.

Using ​http://jsperf.com/id-vs-class-vs-tag-selectors/2 as a benchmark I've compared versions 1.7.2, 1.8.0, 1.8.1, 1.8.2 and some git versions going forwards (12, 16, 17, 18, 22 Oct and 2 Nov).

While there has been significant increase in some selectors; ($('blockquote') has nearly doubled and pseudo ($(':hidden')) is up by 50%. Class selectors (which I would argue are used most) have seen a 50% reduction in speed from 168 operations/sec to an average of 70 ops/sec.

We would dearly like to upgrade to the latest jQuery, however our corporate user base requires us to support IE7.

I have been unable to locate any changes between 1.7.2 and 1.8.0 which may be responsible and sincerely hope somebody here can!

Regards,

John.

[dmethvin]

As we discussed in IRC, various selectors will get slower and faster from version to version. Without seeing the specific code, which you weren't able to share, we can't tell if this is a pathological case or not. The fact that it was a table with more than a thousand entries including form fields tells me that it might be. Staying with 1.7 may be the best solution here.