As of iOS 8 that's no longer the case. JSC JIT compilation can be used in native apps. (It's also used by WKWebView.)

http://trac.webkit.org/wiki/JavaScriptCore

"JavaScriptCore is an optimizing virtual machine. JavaScriptCore consists of the following building blocks: lexer, parser, start-up interpreter (LLInt), baseline JIT, a low-latency optimizing JIT (DFG), and a high-throughput optimizing JIT (FTL)."

Apps can use JavaScriptCore, and JavaScriptCore can use JIT, but these can't happen together, because third-party apps aren't permitted to execute writeable memory.

http://stackoverflow.com/questions/22281265/is-javascriptcor...

This is good to know. Looks like the only way to make use of JIT (by someone who isn't Apple) is to use a WKWebView to execute the JS.

This has been false for years.

I haven't used React Native, but I've done quite a bit with native bridging with JavaScriptCore and v8. If your performance bottlenecks are crossing the Javascript-to-native boundary, JIT can't help you. And crossing the bridge boundary isn't the cheapest operation.

That isn't an issue with React Native, which runs JS on its own thread and implements an asynchronous, batched bridge between JS and native.