>risk runtime type errors. This is the part that's missing. Or more completely there's no runtime types at all. So you can't do stuff like: result = fet

>risk runtime type errors. This is the part that's missing. Or more completely there's no runtime types at all. So you can't do stuff like: result = fetch.... if(result is User){ return result }else{ Throw error } The mechanism TS gives you to do that is essentially recreating all your type rules in a validation. Which is keeping the same information in two places and risks them getting out of sync. Most people pick up a library that generates the types and validations for you to solve this. Which works but it's kind of weird that you have to.