What is in TypeScript?
Describing on above purposely omitted since as Microsoft developers or as a developer above concepts and implementations are not new topics for us.
Develop TypeScript Application
You can be created TypeScript application as below, and you will get solution as shows in the above image which compares ts and js files which included.
File→New→Project→Templates→TypeScript→“HTML Application with TypeScript”
After you done with the templating you can develop your HTML application with using TypeScript and by integrating any client side framework like AngularJs, ReactJS or any framework you prefer. But my personal preference is Angular or React since they equipped with strong community and rich framework background.
You will use Unified APIs or more generally saying RESTful APIs to communicate with Office application data and services. If you are developing on SharePoint you may also use JSOM based libraries but the recommended way is keep the decoupled concerns with the RESTful APIs since it gives many advantages (Note: wait for explore advantages of moving towards RESTful services when Office Dev on a post in near future) .
Converting TypeScript Application to Add-in (App)
After you done with TypeScript Application, converting app to Office Add-in is few step process. You can be pick which Office application and then all done. By clicking on “Start” you can test the application.
Note: If you developing SharePoint Add-in you are requires to give SharePoint, you requires to give relevant information to connect with it to host the application. For other application types you requires only Office installed on the machine to host the application.