What are the limitations of coding web apps for the iPhone?

For instance, could a web app access the mic on an iPhone and transmit voice back to a server?

Or is it possible to build Safari extensions for the iPhone that can operate transparentl开发者_开发百科y on a web page? For instance, is it possible to build an extension that removed ads from Google result pages for the iPhone, without the user clicking any buttons to activate the ad-removal functionality?

You pretty much hit the main limitations.

• You have no access to hardware that's not supported by HTML5 (geolocation is, but things such as acceleration and audio/video recording are not).
• You can't build Safari extensions for the iPhone at this time, you can only use JavaScript like usual.

Some frameworks like PhoneGap make attempts to provide more hardware features via a native app container, but it appears Apple is trying to prevent those apps from going on the App Store, to some extent.