NavigationPreloadManager: setHeaderValue() method

{{APIRef("Service Workers API")}}{{SecureContext_Header}}{{AvailableInWorkers}}

The setHeaderValue() method of the {{domxref("NavigationPreloadManager")}} interface sets the value of the {{HTTPHeader("Service-Worker-Navigation-Preload")}} header that will be sent with requests resulting from a {{domxref("Window/fetch", "fetch()")}} operation made during service worker navigation preloading. It returns an empty {{jsxref("Promise")}} that resolves with undefined.

The presence of the {{HTTPHeader("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.

Syntax

setHeaderValue(value)

Parameters

• value
  • : An arbitrary string value, which the target server uses to determine what should returned for the requested resource.

Return value

A {{jsxref("Promise")}} that resolves with {{jsxref('undefined')}}.

Exceptions

• InvalidStateError {{domxref("DOMException")}}
  • : There is no active worker associated with the registration to which this {{domxref("NavigationPreloadManager")}} belongs.

Examples

The code below demonstrates how the value might be set.

navigator.serviceWorker.ready
  .then((registration) =>
    registration.navigationPreload.setHeaderValue(newValue),
  )
  .then(() => console.log("Done!"))
  .catch((e) =>
    console.error(`NavigationPreloadManager not supported: ${e.message}`),
  );

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}