Managing states with CustomStateSet

[Westbrook]

Currently when wanting to add/delete a CSS Custom State to the CustomStateSet you need to do something like the following:

if (value) {
    this.internals.states.add(state);
} else {
   this.internals.states.delete(state);
}

When a custom element sets out to manage this state once, this is not too big of a deal, however as an author looks to manage this state from more locations you end up wanting for a helper method to support managing this:

setState(state, value) {
    if (value) {
        this.internals.states.add(state);
    } else {
       this.internals.states.delete(state);
    }
}

It's not the most complicated boilerplate required by the various Web Components APIs, but it's an added bit of complexity for authors to spend limited decisions making faculties on. Was there a specific reason not to include a toggle(state, value) method? With this we'd be able to simplify this usage to:

this.internals.states.toggle(state, value);

Would there be room to include such an expansion on the CustomStateSet object?

[keithamus]

See related issue: whatwg/webidl#1370 - it was mentioned that we should see what happens with Set from which the API is based.