A good post on writing a cordova plugin for ios:
https://medium.com/@JordanBenge/how-to-write-an-ionic-cordova-plugin-in-swift-8d443430b27d. Found this particularly useful when migrating a former phonegap app that was written in an older version of cordova to latest version wherein the ios code is in Swift 4. For functions written in older version of swift no annotation was required. However, for cordova integration to work with the Swift 4 migration, had to add the @objc annotation to the class and functions in Swift.
