I've been working with JavaScriptCore to facilitate the optional code-on demand constraint of REST, e.g. A client requests a JS representation of a resource, which includes what fields a valid resource has, type hinting so the client can dynamically build a UITableView with the most appropriate controls for each field, and validation functions allowing the client to validate a field when it changes or when its UITextField resigns first responder status.

I just had a horrifying thought: Aren't apps that download code banned from the App Store? If so, would this include JS downloaded at runtime to be evaluated with JavaScriptCore? What's the conceptual difference between this and a UIWebView opening a page that has <script> tags embedded?