TypeScript-Handbook

// Rest<T> should be equal to Diff, because TS doesn't have exact types type ElementType<T, K extends keyof T> = T[K] // PropertyType in unnecessary, because T[K] works for everything // Note that this is variadic - "Args" is an array of arguments type Call<F, Args extends any[]> = F extends (...args: Args) => infer B ? B : never // This works for both objects and tuples. type ObjMap<T, F> = { [K in keyof T]: Call<F, [T[K]]> } // I couldn't figure out how to implement Class<T>, but you can access the type of a class instance with // typeof ClassName.prototype // $SuperType and $Subtype are not documented, so I can't try to replicate them. // TypeScript doesn't have existential types, but you can emulate them within the type system, or avoid them using e.g "infer" // Discussion and encoding https://github.com/Microsoft/TypeScript/issues/14466#issuecomment-338045331 I don't agree with your statement about TypeScript's design. Before ES6 TypeScript _was_ quite different from JS, but for the past 3 or 4 years it has followed modern JS very closely. The flavor of JS it supports is fully compliant with ES2018, and the ONLY feature with codegen impact it has in addition to modern JS and JSX are enums - which compile down to simple object literals. [1] https://www.typescriptlang.org/docs/handbook/advanced-types.... [2] https://github.com/Microsoft/TypeScript-Handbook/blob/master... [3] https://github.com/facebook/flow/blob/cf03c08109014c4503a392...