The replacesClientId read-only property of the FetchEvent interface is the id of the 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.


var myReplacedClientId = fetchEvent.replacesClientId;


A DOMString.


self.addEventListener('fetch', function(event) {


Specification Status Comment
Service Workers
The definition of 'replacesClientId' in that specification.
Working Draft Initial definition.

Browser compatibility

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See also