Page options

By default, SvelteKit will render any component first on the server and send it to the client as HTML. It will then render the component again in the browser to make it interactive in a process called hydration. For this reason, you need to ensure that components can run in both places. SvelteKit will then initialise a router that takes over subsequent navigations.

You can control each of these on a per-app (via svelte.config.js) or per-page (via +page.js or +page.server.js) basis. If both are specified, per-page settings override per-app settings in case of conflicts.

routerpermalink

SvelteKit includes a client-side router that intercepts navigations (from the user clicking on links, or interacting with the back/forward buttons) and updates the page contents, rather than letting the browser handle the navigation by reloading.

In certain circumstances you might need to disable client-side routing with the app-wide browser.router config option or the page-level router export:

ts
export const router = false;

Note that this will disable client-side routing for any navigation from this page, regardless of whether the router is already active.

hydratepermalink

Ordinarily, SvelteKit hydrates your server-rendered HTML into an interactive page. Some pages don't require JavaScript at all — many blog posts and 'about' pages fall into this category. In these cases you can skip hydration when the app boots up with the app-wide browser.hydrate config option or the page-level hydrate export:

ts
export const hydrate = false;

If hydrate and router are both false, SvelteKit will not add any JavaScript to the page at all. If server-side rendering is disabled in handle, hydrate must be true or no content will be rendered.

prerenderpermalink

It's likely that at least some routes of your app can be represented as a simple HTML file generated at build time. These routes can be prerendered.

Prerendering happens automatically for any +page or +server file with the prerender annotation:

ts
export const prerender = true;

Alternatively, you can set config.kit.prerender.default to true and prerender everything except pages that are explicitly marked as not prerenderable:

ts
export const prerender = false;

Routes with prerender = true will be excluded from manifests used for dynamic SSR, making your server (or serverless/edge functions) smaller. In some cases you might want to prerender a route but also include it in the manifest (for example, you want to prerender your most recent/popular content but server-render the long tail) — for these cases, there's a third option, 'auto':

ts
export const prerender = 'auto';

If your entire app is suitable for prerendering, you can use adapter-static, which will output files suitable for use with any static webserver.

The prerenderer will start at the root of your app and generate HTML for any prerenderable pages it finds. Each page is scanned for <a> elements that point to other pages that are candidates for prerendering — because of this, you generally don't need to specify which pages should be accessed. If you do need to specify which pages should be accessed by the prerenderer, you can do so with the entries option in the prerender configuration.

When not to prerenderpermalink

The basic rule is this: for a page to be prerenderable, any two users hitting it directly must get the same content from the server.

Not all pages are suitable for prerendering. Any content that is prerendered will be seen by all users. You can of course fetch personalized data in onMount in a prerendered page, but this may result in a poorer user experience since it will involve blank initial content or loading indicators.

Note that you can still prerender pages that load data based on the page's parameters, such as a src/routes/blog/[slug]/+page.svelte route.

Accessing url.searchParams during prerendering is forbidden. If you need to use it, ensure you are only doing so in the browser (for example in onMount).

Route conflictspermalink

Because prerendering writes to the filesystem, it isn't possible to have two endpoints that would cause a directory and a file to have the same name. For example, src/routes/foo/+server.js and src/routes/foo/bar/+server.js would try to create foo and foo/bar, which is impossible.

For that reason among others, it's recommended that you always include a file extension — src/routes/foo.json/+server.js and src/routes/foo/bar.json/+server.js would result in foo.json and foo/bar.json files living harmoniously side-by-side.

For pages, we skirt around this problem by writing foo/index.html instead of foo.