Using fromEvent with SignalR hub connection.

[kosmakoff]

I am integrating RxJS with SignalR. SignalR has this type called HubConnection which in turn has 2 jQuery-like events subscription methods on and off.

I tried to pass the instance of HubConnection directly to fromEvent function to create an observable of this connection's events.

The issue is that Typescript won't allow that, because fromEvent expects the handler's type is defined as Function in rxjs, as follows:

export interface JQueryStyleEventEmitter {
    on: (eventName: string, handler: Function) => void;
    off: (eventName: string, handler: Function) => void;
}

Whereas the connections' on method signature looks like this:

on(methodName: string, newMethod: (...args: any[]) => void): void;

Typescript complains about type Function doesn't fit into signature (...args: any[]): void. I'm not that proficient in Typescript to understand whether it is a limitation of Typescript, or shortcoming of RxJS itself.

Any advise, anyone, please?

[voliva]

Yep... it seems like there's something missmatching on the types of Function.

However, you have an easy workaround by using fromEventPattern:

const fromSignalREvent = (connection: HubConnection, eventName: string) =>
  fromEventPattern(
    handler => connection.on(eventName, handler),
    handler => connection.off(eventName, handler)
  )

[cartant]

FWIW, the v7 types won't be using Function:

rxjs/src/internal/observable/fromEvent.ts

Lines 30 to 33 in 105bf99

	export interface JQueryStyleEventEmitter<TContext, T> {
	on: (eventName: string, handler: (this: TContext, t: T, ...args: any[]) => any) => void;
	off: (eventName: string, handler: (this: TContext, t: T, ...args: any[]) => any) => void;
	}

Function is one of those types that's best avoided completely.