Tagged union types [0] are very powerful and let you model most things in very robust ways. type Response<Data, Error = string> = | { type: "Loading" }

Tagged union types [0] are very powerful and let you model most things in very robust ways. type Response<Data, Error = string> = | { type: "Loading" } | { type: "Success", data: Data } | { type: "Error", message: Error } You won't have access to data unless type === "Success". You can model other mutually exclusive situations in the same way. Then, Typescript comes with very handy utility types. [1] And if you're having an especially good day, you can loose yourself in type level programming. Mapped types, for example. [2] Though this is only really necessary at a library level. Back in reality, type narrowing [3] and function overloading [4] are good to know about. And there's a lot more. - 0 https://mariusschulz.com/blog/tagged-union-types-in-typescript https://mariusschulz.com/blog/tagged-union-types-in-typescri... - 1 https://www.typescriptlang.org/docs/handbook/utility-types.html https://www.typescriptlang.org/docs/handbook/utility-types.h... - 2 https://www.typescriptlang.org/docs/handbook/2/mapped-types.html https://www.typescriptlang.org/docs/handbook/2/mapped-types.... - 3 https://www.typescriptlang.org/docs/handbook/2/narrowing.html https://www.typescriptlang.org/docs/handbook/2/narrowing.htm... - 4 https://www.typescriptlang.org/docs/handbook/2/functions.html#function-overloads https://www.typescriptlang.org/docs/handbook/2/functions.htm...