When working with TypeScript-first libraries like Prisma, you'll be working with functions that have useful, but complex type signatures. The TypeScript built-in Utility Types make a big difference when working with these.
For instance, a function that makes a couple Prisma calls with join'ed data will have a large return type that you can't easily recreate with imported types from the Prisma client.
Given a function like this, we can start out extracting its return type with
the
ReturnType
utility type, passing it the typeof the function as the generic.
type FuncReturnType = ReturnType<typeof getPostsForUser>A function like this is going to be async, so its return type will be wrapped
in a promise. We can "unwrap" the promise with
Awaited.
type FuncReturnType = ReturnType<typeof getPostsForUser>
type ResolvedFuncReturnType = Awaited<FuncReturnType>We are often querying for lists of things, so the result will be an array of
the type we are interested in. We can extract the type of an array with
[number].
type FuncReturnType = ReturnType<typeof getPostsForUser>
type ResolvedFuncReturnType = Awaited<FuncReturnType>
type PostType = ResolvedFuncReturnType[number]Putting it all together into a single line looks like this:
type Post = Awaited<ReturnType<typeof getPostsForUser>>[number]