[smt88]

The good thing about TS is that you can add types gradually. I actually think there's a lot of value in adding the typing manually because A) you're guaranteed to find bugs, and B) you have to revisit your assumptions with the advantage of hindsight.

[clarus]

With Flow you can also add types gradually. Actually, one of the reasons why Facebook created Flow is that they thought that TypeScript was not "gradual enough". A good presentation on how Flow differs from other type systems: https://www.youtube.com/watch?v=VEaDsKyDxkY