The setHeaderValue()
method of the NavigationPreloadManager
interface sets the value of the Service-Worker-Navigation-Preload
header that will be sent with requests resulting from a fetch()
operation made during service worker navigation preloading. It returns an empty Promise
that resolves with undefined
.
The presence of the Service-Worker-Navigation-Preload
header in preloading requests allows servers to configure the returned resource differently for preloading fetch requests than from normal fetch requests. The default directive is set to true
: this method allows the possibility of configuring multiple different responses to preload requests.
Note: If a different response may result from setting this header, the server must set Vary: Service-Worker-Navigation-Preload
to ensure that the different responses are cached.