Add default callback to fx.prepend method

[sergeysova]

Motivation

Sometimes I need to call effect from my React-components. WebStorm shows me a warning about "unhandled promise" (Promise returned from myFx is ignored), because I call effect in event handler, without await. IDE assumes that promise can be rejected, and in Node.JS environment it can be "unhandled promise rejection" and terminate process, but IDE don't know about that fix in effect source code.

Current solution

I creates a new event from effect using .prepend with noop callback or identity-callback, but typescript don't like identity-callback if effect has no arguments, also prepend requires to set type for callback argument, that annoying.

const foo = fxWithoutArgs.prepend(() => {});
// and
const bar = generalFx.prepend(args => args);

Suggestion

I suggest to add default callback arg => arg and add types for typescript, to allow void params.

const foo: Event<void> = fxWithoutArgs.prepend();
// and
const bar: Event<Params> = generalFx.prepend();

[zerobias]

As we artificially forced promise returned by effect to be always handled, I'm suggest to ask jetbrains to allow exceptions for their linting, because changing runtime and introducing additional complexity to just cool down a thing builded to help us is not an optimal way to fix issues

[doasync]

I just write:
void getDataFx()
according to my linter rules in order to indicate that promise is ignored intentionally