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/**
* Describes the different fallback modes that a given page can have.
*/
export const enum FallbackMode {
/**
* A BLOCKING_STATIC_RENDER fallback will block the request until the page is
* generated. No fallback page will be rendered, and users will have to wait
* to render the page.
*/
BLOCKING_STATIC_RENDER = 'BLOCKING_STATIC_RENDER',
/**
* When set to PRERENDER, a fallback page will be sent to users in place of
* forcing them to wait for the page to be generated. This allows the user to
* see a rendered page earlier.
*/
PRERENDER = 'PRERENDER',
/**
* When set to NOT_FOUND, pages that are not already prerendered will result
* in a not found response.
*/
NOT_FOUND = 'NOT_FOUND',
}
/**
* The fallback value returned from the `getStaticPaths` function.
*/
export type GetStaticPathsFallback = boolean | 'blocking'
/**
* Parses the fallback field from the prerender manifest.
*
* @param fallbackField The fallback field from the prerender manifest.
* @returns The fallback mode.
*/
export function parseFallbackField(
fallbackField: string | boolean | null | undefined
): FallbackMode | undefined {
if (typeof fallbackField === 'string') {
return FallbackMode.PRERENDER
} else if (fallbackField === null) {
return FallbackMode.BLOCKING_STATIC_RENDER
} else if (fallbackField === false) {
return FallbackMode.NOT_FOUND
} else if (fallbackField === undefined) {
return undefined
} else {
throw new Error(
`Invalid fallback option: ${fallbackField}. Fallback option must be a string, null, undefined, or false.`
)
}
}
export function fallbackModeToFallbackField(
fallback: FallbackMode,
page: string | undefined
): string | false | null {
switch (fallback) {
case FallbackMode.BLOCKING_STATIC_RENDER:
return null
case FallbackMode.NOT_FOUND:
return false
case FallbackMode.PRERENDER:
if (!page) {
throw new Error(
`Invariant: expected a page to be provided when fallback mode is "${fallback}"`
)
}
return page
default:
throw new Error(`Invalid fallback mode: ${fallback}`)
}
}
/**
* Parses the fallback from the static paths result.
*
* @param result The result from the static paths function.
* @returns The fallback mode.
*/
export function parseStaticPathsResult(
result: GetStaticPathsFallback
): FallbackMode {
if (result === true) {
return FallbackMode.PRERENDER
} else if (result === 'blocking') {
return FallbackMode.BLOCKING_STATIC_RENDER
} else {
return FallbackMode.NOT_FOUND
}
}
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