Method from

src/Observable.js:265–304

(x)

    // == Derived ==

    static from(x) {

        let C = typeof this === "function" ? this : Observable;

        if (x == null)
            throw new TypeError(x + " is not an object");

        let method = getMethod(x, Symbol.observable);

        if (method) {

            let observable = method.call(x);

            if (Object(observable) !== observable)
                throw new TypeError(observable + " is not an object");

            if (observable.constructor === C)
                return observable;

            return new C(observer => observable.subscribe(observer));
        }

        method = getMethod(x, Symbol.iterator);

        if (!method)
            throw new TypeError(x + " is not observable");

        return new C(observer => {

            for (let item of method.call(x)) {

                observer.next(item);

                if (observer.closed)
                    return;
            }

            observer.complete();
        });
    }

    static of(...items) {