the big problem is that Service Workers are not always running. When the app is idle or device resources are constrained, the SW may be terminated by the browser. When you return the fetches are no longer intercepted by the SW. Also, SW can only intercept same-origin fetches. Cross-origin requests, for example, images from a different domain do not arrive at SW. You can of course add the token in the fetch calls in your JavaScript and ditch the SW to only use it as a cache.