In short: very good things
iOS 8 is the most significant update "since the launch of the App Store" according to Apple. There's a ton of improvements and features that have been added, but I won't be talking about them here. What we are interested in is how this will affect the development and performance of our HTML5 mobile applications.
An image from icanuse.com that highlights the vast difference between iOS 7 and iOS 8 has been doing the rounds on Twitter:
— Paul Irish (@paul_irish) September 18, 2014
I highly recommend checking out this in depth analysis by Ross Gerbassi over at Sencha, Ross goes into a lot more depth than I possibly could.
Perhaps the most exciting addition for HTML 5 mobile app developers is the introduction of the new WKWebView. WKWebView will replace the standard UIWebView (although UIWebView will still be available), UIWebView is the native web view that is used to display your application. WKWebView includes the NitroJS engine which has at least 4x the performance of UIWebView.
BUT you can't actually use WKWebView yet due to some unfortunate bugs, you can read more about the specifics at the Sencha blog. Hopefully these will be fixed soon.
These are really exciting times for web and hybrid app developers. With technologies like Sencha Touch, Famo.us and Ionic constantly pushing the limits of what we can do and browsers constantly improving we can expect to see some really cool things in the near future.