I use https://github.com/gcanti/io-ts https://github.com/gcanti/io-ts for the runtime checking. It is similar to tcomb (same author)! You can even define the t

I use https://github.com/gcanti/io-ts https://github.com/gcanti/io-ts for the runtime checking. It is similar to tcomb (same author)! You can even define the type via io-ts and then make a TypeScript interface out of it! Given this, and the other libraries that do something similar, I am not sure why Microsoft needs to add it to the language.