Xamarin : with one year of experience, I realized that this is a truly flexible development environment. The amazing part about Xamarin is that you have 2 options: i) go to your native ii) go to the cross platform, it makes it open, what use do you prefer and how do you want to do it.
OS Support / Deployment on: Windows, iOS, Android, Mac
Languages Used: XML, C #
Ionic : especially Ionic-2. This is awesome for all users of HTML, CSS and JS to create applications for web applications, mobile applications. I have not seen its deployment for a Windows phone (if so, then I'm not sure). With Ionic, forget all your structured MVVM coding. But a new version-2 implementation parallel to angular -2 (typescript) could implement.
OS Support / Deployment on: iOS, Android, Web (HTML / CSS)
: HTML, CSS, angular -2
Xamarin - Dev - 4/5 IDE . Xamarin. .
Ionic-2 - Mobile Web Dev - 3/5 . , .
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