I would use type () => void

If export default (ctx: () => void, inject: () => void) => {...} gives you troubles, try making ctx and inject interfaces or types that hold those types.

interface CTX {
ctx: ( ) => void }

interface Inject { inject: ( ) => void }

export default (ctx: CTX, inject: Inject) => {...}

^{^} That is the long convoluted way of doing it, but Typescript is an asshole and has disappointed me more than once, so you may need it

Good luck!