I’m pleased to let you know that when the ArcGIS API 4 was released, the new TypeScript definition files for 4.0 were also released.
Because of all the interest and questions I’ve gotten about using the definition files, I thought it would be worth putting together a short video on a sample application using the definition files.
You can find the repo for the sample application on github. This repo is using .tsx files, which means that they are TypeScript files with JSX inside them. You can learn more about this here. TypeScript has it’s own compiler to turn TS to ES5, and a really cool feature is being able to compile the JSX to ES5 for React components.
You can find info on the dojo/typings here.
You can learn more about the typings command line tool here.
There are some great short videos on TypeScript at TypeScript-Tacos!
I would highly recommend the Definitive TypeScript Guide on SitePen. SitePen has been doing some pretty great development with TypeScript, including providing valuable feedback to the TypeScript team.
You can also check out some pretty awesome TypeScript code in the Dojo 2 repos, like dojo/core to get an idea of some of the cool stuff you can do with TypeScript.
Although, I have not come across a TypeScript book yet, mostly since it updates so quickly, I have found Type-Driven Development with Idris to be a great book and a great language to really embrace types. It’s helped me to become a better TypeScript developer, so I would recommend it as an adjacent resource.