Service worker cache wrapper that lets you use arbitrary cache keys

serviceworker-cache-wrapper.js

function cachePut(key, request, response) {
    caches.open(key).then(function(cache) {
        cache.put(request, response);
    });
}
function cacheGet(key) {
    return new Promise(function(resolve, reject) {
        caches.open(key).then(function(cache) {
            cache.keys().then(function(keyArray) {
                if (keyArray.length) {
                    cache.match(keyArray[0]).then(function(response) {
                        resolve(response);
                    });
                }
                else {
                    resolve(null);
                }
            });
        });
    });
}

See http://www.holovaty.com/writing/service-worker-cache-names/ for explanation.