There are so many better options if you want a good type system (Elm, PureScript, Rescript, GHCjs, Scala.js, and many more). TypeScript is unsound, and necessarily by it's design, it has to take on weird issues to maintain compatibility with JavaScript (null/undefined, can run effect anywhere, a lot of codebases are filled with any types). Heck, TypeScript doesn't even come with ADTs and proper pattern matching.