const lazyCacheObject = new LazyCacheObject({
    initKey(key) {
        // do some ASYNC work and return a Promise
        // this function will be called every time there will be request for the key
        // and cache will be empty
        return asyncPromiseReturn()
    },
    shouldInvalidate(key, value) {
        // this is optional
        // you can decide if you want the cache to be invalidated after TTL
        // you should return a boolean or a promise for a boolean
        // this function will be called every time LazyCacheObject will try
        // to invalidate the key.
        return true;
    },
    onShouldInvalidateError(err) {
        // this one is optional as well
        // it's called anytime shouldInvalidate throws an error
        console.error('an error ocured', err);
    }
});

// to get a key from the cache just call `get` it will return a promise for the value
lazyCacheObject.get('some-key').then(value => {
    // here you have your value.
});

lazyCacheObject.startCacheInvalidationTimer(60000);
// takes one argument: timeToLiveInMilliseconds
// the above method will make LazyCacheObject invalidate old keys every minute
// it will not invalidate a key if `shouldInvalidate()` method has returned false for that key
// it will run a function to check if any of the keys are to be dropped every timeToLiveInMilliseconds / 4 milliseconds
// so your item can live in the cache for a maximum of 5/4 * timeToLiveInMilliseconds milliseconds

lazyCacheObject.stopCacheInvalidationTimer();
// from now on, no invalidation will happen - internal `setInterval` method is cleared.