cycle/dom stream library specific typings

As discussed in point (4) of #307 regarding Typescript typings, @cycle/dom’s (RC) DOMSource.events() returns any. This is done intentionally, as cycle’s future is to be stream library agnostic, i.e. it should be able to be used with xstream, RxJS, most, etc.

However from an application developer’s point of view, DOMSource.events() would ideally return the type appropriate to the stream library (in xstream’s case Stream<Event>), as this will help with compile time and edit time error checking and intellisense.

This issue is not specific to @cycle/dom. Any cyclejs driver which is stream library agnostic would have a similar problem. Solving this issue for @cycle/dom would set a common approach for all cyclejs drivers.

On approach would be to create a set of typings specific to each stream library. For example, for @cycle/dom, I have a simplified set of typings in my application’s custom-typings directory:

import { IDOMSource, EventsFnOptions } from '@cycle/dom';
import { Stream } from 'xstream';

declare module '@cycle/dom' {
    export class DOMSource {
        select(selector: string): DOMSource;
        events(eventType: string, options?: EventsFnOptions): Stream<Event>;
    }
}

This issue is to discuss the best and most convenient options for solving this typings issue for cyclejs drivers.

[staltz]

We can’t seem to find how to automagically make DOMSource know which stream library type it is returning via events(). That would be the ideal case, but we are hitting the limits of TypeScript. So which of these two options seems the least worst?

(1) DOMSource is a generic and you need to tell what are the types it returns when calling events() and elements: DOMSource<Stream<Event>, Stream<Element>>. This would need to be typed anywhere we have a function that expects a DOMSource. React with 👍 if you want this option.

(2) A custom typings file similar to what you made, but it would have to be imported separately and included via typings for instance. After that, everything works automagically. React with ❤️ if you want this option.

[staltz]

I believe this issue is now solved with

    "@cycle/dom": "10.0.0-rc30",
    "@cycle/http": "9.0.0-rc8",

and solution (3).

Check out these examples: https://github.com/cyclejs/examples/tree/diversity/http-random-user https://github.com/cyclejs/examples/tree/diversity/bmi-typescript

So far, only @cycle/...../xstream-typings is available, but making rxjs-typings etc should be straight-forward, we will do that next.