NavigationPreloadManager: setHeaderValue() method

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Note: This feature is available in Web Workers.

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.

Syntax

js
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 Promise that resolves with undefined.

Exceptions

InvalidStateError DOMException

There is no active worker associated with the registration to which this NavigationPreloadManager belongs.

Examples

The code below demonstrates how the value might be set.

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

Specifications

Specification
Service Workers
# dom-navigationpreloadmanager-setheadervalue

Browser compatibility

BCD tables only load in the browser