Is JavaScriptCore framework on iOS 7 using JIT compilation?

Question

Based on some googling it seems like JavaScript on ios is JIT compiled sometimes and sometimes not. How about the JavaScriptCore framework that got added in ios 7? Will I get JIT compilation if I use that in my app?

Answer 1

No, JavaScriptCore on iOS 7+ won't be able to JIT compile for you, because iOS disallows mapping writable/executable pages of memory as a hard rule, and that's a requirement for JIT. Only MobileSafari.app, Web.app and a handful of other system apps carry an entitlement that allows them to JIT compile. The new WKWebView in iOS 8 is rendered in a separate process that is allowed to JIT compile, so JavaScript in a WKWebView is faster than a UIWebView or plain JSContext.