Convert Web Extension to Safari App Extension

I have Web Extensions which currently runs on Chrome, Firefox and Opera. Now I'm wondering is there a way to use same code to build Safari App Extension, maybe something like PhoneGap(wrap all existing JS code in Safari App Extension project) or there are limitations like tabs handling for javascript and some things just have to be written in native code.

Thanks

You should be able to reuse Content Scripts from your Web-Extensions (but you need to rewrite code to be able to send/receive messages with "background"). Background script will have to be re-written in Swift or Objective-C.

You need to developp:

• a Mac Host Application (which will be a companion to the Extension) : Swift or Objective-C (this app must have minimum features to pass Apple review - check the Apple guidelines for Mac Apps)
• the extension : in Swift or Objective-C + HTML/JS (as for other browsers) The code in Swift (or Obj-C) for the extension is the equivalent of the background page you have in Web Extensions. It will control the toolbar button, life-cycle of the extension and can talk with injected scripts.

You have an (small) example on Apple website : https://developer.apple.com/documentation/safariservices/safari_app_extensions?changes=_2&language=objc

You should not use Extension Builder anymore (accessible from Developer menu in Safari) since this is for legacy (pure JS) extensions only. So you need to get in XCode.

Last thing, but not least... Safari App Extensions, compared to Safari legacy extensions, are "a bit" more limited (for instance, you won’t be able to open the toolbar popup programmatically, just as with Chrome web-extensions actually).