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0 pointsmwcampbell10y ago0 comments

Do you have anything to back that up?

0 comments

Run some lists with images on them on iPhone 5. Anecdotal, and I am sure you can dig into metal to improve performance, but out of the box, it's kinda poor. I still like React and I'm hopeful React-Native will improve.

mwcampbellOP10y ago

Thanks. I wonder how much of that is due to the fact that JavaScriptCore can't use JIT compilation when running in an iOS application other than Safari.

andrewjl10y ago

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)."

DerekL10y ago

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...

1 more reply

zepto10y ago

This has been false for years.

ewmailing10y ago

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.

mwcampbellOP10y ago

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.

j / k navigate · click thread line to collapse

0 comments

seivan10y ago

mwcampbellOP10y ago

Thanks. I wonder how much of that is due to the fact that JavaScriptCore can't use JIT compilation when running in an iOS application other than Safari.

andrewjl10y ago

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

DerekL10y ago

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...

1 more reply

zepto10y ago

This has been false for years.

ewmailing10y ago

mwcampbellOP10y ago

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.

j / k navigate · click thread line to collapse