@ces/observable-state/lib/observable-state.js

A type of Observable that holds state that can be consumed synchronically / imperatively.

import { Observable } from 'rxjs';
// This class is used to turn an Observable into something quite like a BehaviorSubject, with
// the exceptions that it can be directly created from an Observable and it doesn't expose an
// observer interface.
//
// Its intended purpose is to turn BehaviorSubjects or other Observable subtypes that emit
// synchronously back into something that can be read imperatively / synchronously after
// they have been piped and thus become regular Observables, losing their ability to be
// consumed imperatively / synchronously.
export class ObservableState extends Observable {
    constructor(o, owner) {
        super((subscriber) => o.subscribe(subscriber));
        this.owner = owner;
        this.getValue = () => this.value;
        this.innerSubscription = this.subscribe(value => this.value = value);
    }
    static from(observable, owner) {
        return new ObservableState(observable, owner);
    }
    static release(owner) {
        if (ObservableState.instances.has(owner)) {
            const ownerSet = ObservableState.instances.get(owner);
            const ownerArray = Array.from(ownerSet);
            for (const instance of ownerArray)
                instance.release();
        }
    }
    static track(instance, owner) {
        if (!ObservableState.instances.has(owner))
            ObservableState.instances.set(owner, new Set());
        ObservableState.instances.get(owner).add(instance);
    }
    static untrack(instance, owner) {
        if (ObservableState.instances.has(owner)) {
            const ownerSet = ObservableState.instances.get(owner);
            ownerSet.delete(instance);
            if (!ownerSet.size)
                ObservableState.instances.delete(owner);
        }
    }
    release() {
        this.innerSubscription.unsubscribe();
        ObservableState.untrack(this, this.owner);
    }
}
ObservableState.instances = new Map();
export const os = (observable, owner) => ObservableState.from(observable, owner);