js / lamport lock with promises

app.js

function uuidv4() {
  return ([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g, c =>
    (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
  );
}

function lamportMutex(id) {
    const X = '_lock-X',
          Y = '_lock-Y';

    const set = (k, v) => localStorage.setItem(k, v),
          get = (k) => localStorage.getItem(k),
          isFree = (k) => {
              let v = get(k);
              return v === undefined || v === null;
          };

    return {
        acquire: function() {
            return this.lock(0);
        },
        release: function() {
            set(Y, null);
        },
        lock: function(retries) {
            const retry = (resolve, reject) => {
                window.requestAnimationFrame(() => {
                    this.lock(retries + 1).then(resolve, reject);
                });
            };
            set(X, id);
            return new Promise((resolve, reject) => {
                if (isFree(Y) || retries > 100) {
                    set(Y, id);
                    if (get(X) === id) {
                        resolve();
                    } else {
                        window.requestAnimationFrame(() => {
                            if (get(Y) === id) {
                                resolve();
                            } else {
                                retry(resolve, reject);
                            }
                        });
                    }
                } else retry(resolve, reject);
            });
        }
    };
}


const mtx = lamportMutex(uuidv4());

// start requesting a new token every second
setInterval(() => {mtx.acquire().then(
    () => {
        console.log('getTokenSilently');
        a0.getTokenSilently({timeoutInSeconds: 5}).then((t) => mtx.release());
    });
}, 500);