Headers: Service-Worker-Navigation-Preload

Service-Worker-Navigation-Preload header

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

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See full compatibility

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 NavigationPreloadManager.setHeaderValue() (and NavigationPreloadManager).

Header type	Request header
Forbidden request header	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, using NavigationPreloadManager.setHeaderValue().

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 NavigationPreloadManager.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

Specification
Service Workers Nightly> # handle-fetch>

Browser compatibility

	Desktop					Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS
`Service-Worker-Navigation-Preload`	59	18	preview97	46	15.4	59	No	43	15.4	7.0	59	15.4