simple caching layer case, not possible?

[EmielM]

I'm trying to implement a very simple caching layer:

function myFetch(url, invalidate) {
    if (!invalidate) {
        return FetchBlob.config({ fileCache: true, key: 'cache'+url }).fetch('GET', url);
    } else {
        // ...?
    }
}

How would I instruct FetchBlob not to look at the FS when making the request, but saving the result there none the less? I don't want to delete the cache file beforehand (which would be tedious btw, because I need to copy the md5 behavior of the key->path implementation?!), because if the request fails I still want to keep the stale version.

Any thoughts?

[EmielM]

I must say that the options fileCache, path and key are very confusing.

If I read the source, serving files from the fs-cache without hitting the network can only be done with the key property: in other words, it's impossible to use the fs layer as a cache with path, right?