FYI, info@yellowla.com seems to be down. Tried to reach you and got the following response:

Message not delivered

Your message couldn't be delivered to info@yellowla.com because the remote server is misconfigured. See technical details below for more information.

The response from the remote server was:

550 5.7.1 Relaying denied

Final-Recipient: rfc822; info@yellowla.com

Action: failed

Status: 5.7.1

Diagnostic-Code: smtp; 550 5.7.1 Relaying denied

Last-Attempt-Date: Wed, 23 May 2018 15:13:45 -0700 (PDT)

Incidentally, so is application@yellowla.com

Message not delivered

Your message couldn't be delivered to application@yellowla.com because the remote server is misconfigured. See technical details below for more information.

The response from the remote server was:

550 5.7.1 Relaying denied

An email idea is on the way, via post.

Is it true that React Native cannot be integrated with an existing Swift/Obj-C codebase?

For example, say that you want to implement login/register on top of an existing Swift codebase. This is possible, right?

(May not have understood OP correctly.)

It depends what you mean 'on top of'. If you mean adding some RN to an existing app, that is conceptually easy but practically quite messy (https://facebook.github.io/react-native/docs/integration-wit...).

If you mean adding native modules into an essentially RN app, that's practically very simple (https://facebook.github.io/react-native/docs/native-modules-...) but still requires some conceptual care (like any API design).

Nvm! It is possible:

https://facebook.github.io/react-native/docs/integration-wit...

You can use 5 line of code to push uiviewcontroller from xib or storyboard. Easier than encapsulate native code to library rn. Xamarin cannot do that

Is truly hard. And not even thing in use it for Xamarin or something else.

I love to have a react-native-like for just the UI and do my code on swift/F# for the rest.

It's definitely possible but hard to do well; dependency management is a pain.