jquery/jquery — comment on commit 3ad0ba62f03ff3d7aec7d3dfb25492cdf33350a7
File:  line 0
By timmywil:

Passing as an argument to typeof avoids the arbitrary execution of the given function in IE and has the added bonus of being noticeably faster than using the `in` operator. Using typeof vs. solely checking for property existence does not actually differ in performance enough to be a concern, according to what we've seen. http://jsperf.com/in-vs-typeof