http header
Service-Worker-Navigation-Preload header
The HTTP Service-Worker-Navigation-Preload request header indicates that the request was the result of a fetch() operation made during service worker navigation preloading.
It allows a server to respond with a different resource than for a normal fetch().
If a different response may result from setting this header, the server must include a Vary: Service-Worker-Navigation-Preload header in responses to ensure that different responses are cached.
For more information see setHeaderValue() (and NavigationPreloadManager).
| Header type | [Request header](https://developer.mozilla.org/en-US/docs/Glossary/Request%20header) |
|---|---|
| [Forbidden request header](https://developer.mozilla.org/en-US/docs/Glossary/Forbidden%20request%20header) | No |
Syntax
Service-Worker-Navigation-Preload: <value>
Directives
<value>- : An arbitrary value that indicates what data should be sent in the response to the preload request.
This defaults to
true. It maybe set to any other string value in the service worker, usingsetHeaderValue().
- : An arbitrary value that indicates what data should be sent in the response to the preload request.
This defaults to
Examples
Service worker navigation preloading headers
The following request header is sent by default in navigation preload requests:
Service-Worker-Navigation-Preload: true
The service worker can set a different header value using setHeaderValue().
For example, in order to request that a fragment of the requested resource be returned in JSON format, the value could be set with the string json_fragment1.
Service-Worker-Navigation-Preload: json_fragment1
Specifications
Browser compatibility
See also
- HTTP Caching: Vary and
Varyheader - Service Worker API