_error.page.js

The page _error.page.js is rendered when an error occurs:

• When no page matches the URL (acting as a 404 page).
• When a .page.js / .page.server.js / .page.route.js file throws an error (acting as a 500 page).

vite-plugin-ssr automatically sets pageContext.pageProps.is404: boolean which allows us to decided whether to show a 404 or 500 page. (Normally pageContext.pageProps is completely defined/controlled by you and vite-plugin-ssr's source code doesn't know anything about pageContext.pageProps but this is the only exception.)

We can define _error.page.js like any other page and create _error.page.client.js and _error.page.server.js.