A cute typescript async lock class I scribbled down

AsyncLock.ts

// You can either use lock() and get a function that releases the lock, or you could use lockAndRun() to wrap around a function! Amazing!
class AsyncLock {
    private promises = new Map<string, Promise<void>>();

    public async lock(key: string): Promise<VoidFunction> {
        if (this.promises.has(key)) {
            await this.promises.get(key);
        }
        let release: VoidFunction;
        const lockPromise = new Promise<void>(resolve => {
            release = () => {
                resolve();
                this.promises.delete(key);
            };
        });

        this.promises.set(key, lockPromise);

        return release!;
    }

    public async lockAndRun<R, F extends () => Promise<R>>(key: string, fn: F): Promise<R> {
        const release = await this.lock(key);
        try {
            return await fn();
        } finally {
            release();
        }
    }
}