This is to help guard against types that can be undefined since the
recommended eslint rules recommend against using `!` operator on values
like:
const obj: Obj | undefined = ...
obj!.value
Now we can use:
const obj: Obj | undefined = ...
const obj2: Obj = guard(isDefined, obj)
obj.value
The guard function will throw an error if obj parameter is undefined.
As seen in TeamService2.ts, the Contextual type will add Context as the
last argument to any method of the interface, as long as the method has
0-4 arguments.
Interfaces with more than 4 arguments cannot use this type, but they
could be converted to interfaces which use 1 argument
(object/dictionary) only.
Some long-term thinking: Maybe only methods with a single argument
should be supported, similar to the way gRPC does it.
A few notes:
1) The context higher-order function will be tedious to define - a lot
more typing than just an extra function argument.
2) As some methods do not require the context function, forgetting to
call it might introduce bugs (await fn will not error out), but
compile checks of the return value type might detect this
Possible solution is to go the GRPC way and allow only a single method
type as a parameter so all server-side method types would look like:
async fn(param: IParam, context: Context) {}
and all client-side method types would look like:
async fn(param: IParam) {}
However, This would deviate from the JSON-RPC standard which allows
multiple arguments to be passed in an array.
Alternatively, context could be passed as a first argument and then
filtered out:
type Arguments<T> = T extends (context: Ctx, ...args: infer A) => infer R
? A
: never
In this case, the type of Ctx would need to be known in advance. Will
have to think about this some more.
Also fix CSRF token. This was probably broken since csurf middleware was
modified to use cookie instead of session storage to provide support for
single page app (SPA).
