Async XML generation

const master = new class {
    constructor() {
        this.done = false;
        this.listeners = [];
    }

    async* makeGenerator(filterCallback) {
        while (true) {
            const {element, resolve} = await new Promise((resolve, reject) => {
                this.listeners.push(resolve);
            });

            if (element === null) {
                resolve();
                break;
            }

            if (filterCallback(element)) {
                yield Promise.resolve(element);
            }

            resolve();
        }
    }

    subscribe(element) {
        const promise = Promise.all(this.listeners.map(listener => {
            return new Promise(resolve => {
                listener({element, resolve});
            });
        }));
        this.listeners = [];
        return promise;
    }

    complete() {
        this.subscribe(null);
    }
}();

for (let space of ["a", "b"]) {
    (async function () {
        const result = [];
        console.log("start", space);
        for await (let object of master.makeGenerator(element => element.char === space)) {
            console.log("space", object);
            result.push(object);
        }
        console.log("end", space);
        console.log(result);
    })();
}
console.log('test');

const data = [
    1, 1, 1, 2, 1, 2, 2, 2, 1, 2, 2, 1, 1, 1, 2, 2, 1, 2, 1, 2,
].map((number, index) => ({char: number === 1 ? "a" : "b", index}));

(async function () {
    for (let element of data) {
        console.log("element", element);
        await master.subscribe(element);
    }
    master.complete();
})();