Automatic type inference for fetched data, using generics and `infer`

delicious.ts

async function getPageData () {
  const users = await get('/users')
  const user1 = await get('/users/1')
  const usersWithParams = await get('/users?limit=10')
  const user1WithParams = await get('/users/1?hello=world')

  return {
    users,
    user1,
    usersWithParams,
    user1WithParams,
  }
}

async function get<Endpoint extends AnyEndpoint> (
  endpoint: Endpoint
): Promise<ResponseJson<Endpoint>> {
  const response = await fetch(`/api${endpoint}`)
  return await response.json()
}

type AnyEndpoint = `/${keyof ResponseJsonByEndpoint}/${number}?${string}`
  | `/${keyof ResponseJsonByEndpoint}/${number}`
  | `/${keyof ResponseJsonByEndpoint}?${string}`
  | `/${keyof ResponseJsonByEndpoint}`

type ResponseJson<Endpoint extends AnyEndpoint> =
  Endpoint extends `/${infer E extends keyof ResponseJsonByEndpoint}/${number}?${string}`
  ? ResponseJsonByEndpoint[E][number]
  : Endpoint extends `/${infer E extends keyof ResponseJsonByEndpoint}/${number}`
  ? ResponseJsonByEndpoint[E][number]
  : Endpoint extends `/${infer E extends keyof ResponseJsonByEndpoint}?${string}`
  ? ResponseJsonByEndpoint[E]
  : Endpoint extends `/${infer E extends keyof ResponseJsonByEndpoint}`
  ? ResponseJsonByEndpoint[E]
  : never

interface ResponseJsonByEndpoint {
  'users': User[],
  'tasks': Task[],
}

interface User {
  id: number,
  name: string,
  password: 'password',
}

interface Task {
  id: number,
  name: string,
}