start-timer.ts

/**
 * Drains the source observable till it completes, and then posts a new value-observable.
 */
function drain<T>(value: T | Observable<T> | (() => T | Observable<T>)) {
    const v = () => {
        const a = typeof value === 'function' ? value.call(null) : value;
        return a instanceof Observable ? a : of(a);
    }
    return s => defer(() => s.pipe(filter(_ => false), c => concat(c, v()))) as Observable<T>;
}

function startTimer() {
    return drain(Date.now);
}

// SEE: https://stackoverflow.com/questions/69472548/remap-rxjs-observable-to-a-timer-start-without-stream-interruption