I was reading a source code about next-firebase-auth.
I am confused about the following code syntax
export const useAuthUser: () => AuthUserContext
export const verifyIdToken: (token: string) => Promise<AuthUser>
The right side look like an arrow function. The left side is declaring varibles. Intuitively, I am thinking is the same as the following:
export const useAuthUser = () => AuthUserContext
However, it doesn't. I did some test on Chrome console. Here is the code
adder : () => (a + b)
When I hit enter, it shows
() => (a+b)
But If I type adder, it shows
Uncaught ReferenceError: adder is not defined
I looked other posts here. It seems like the colon (:) is related to type annotation. So does it mean the right side is a type or interface? But how is an arrow function type or interface? It does not make sense.
Thanks for your help!
The stuff after the colon is the type. As a type, () => AuthUserContext means a function that doesn't require any arguments, and which returns an AuthUserContext. (token: string) => Promise<AuthUser> Means a function that requires a single argument which is a string, and then returns a Promise that will resolve to an AuthUser
The lines of code you showed seem incomplete. Typically, a const will immediately followed by an assignment, as in:
export const useAuthUser: () => AuthUserContext = () => {
// some code which returns an AuthUserContext
}
I did some test on Chrome console.
The console only supports javascript, not typescript