files/en-us/web/api/fetchevent/replacesclientid/index.md
{{APIRef("Service Workers API")}}{{AvailableInWorkers("service")}}
The replacesClientId read-only property of the
{{domxref("FetchEvent")}} interface is the {{domxref("Client.id", "id")}} of the
{{domxref("Client", "client")}} that is being replaced during a page navigation.
For example, when navigating from page A to page B replacesClientId is the
ID of the client associated with page A. It can be an empty string when navigating from
about:blank to another page, as about:blank's client will be
reused, rather than be replaced.
Additionally, if the fetch isn't a navigation, replacesClientId will be an
empty string. This could be used to access/communicate with a client that will
imminently be replaced, right before a navigation.
A string.
self.addEventListener("fetch", (event) => {
console.log(event.replacesClientId);
});
{{Specifications}}
{{Compat}}