SvelteKitAdvanced

Advanced routing

Rest parameters

If the number of route segments is unknown, you can use rest syntax — for example you might implement GitHub’s file viewer like so...

/[org]/[repo]/tree/[branch]/[...file]

...in which case a request for /sveltejs/kit/tree/main/documentation/docs/04-advanced-routing.md would result in the following parameters being available to the page:

{
	org: 'sveltejs',
	repo: 'kit',
	branch: 'main',
	file: 'documentation/docs/04-advanced-routing.md'
}

src/routes/a/[...rest]/z/+page.svelte will match /a/z (i.e. there’s no parameter at all) as well as /a/b/z and /a/b/c/z and so on. Make sure you check that the value of the rest parameter is valid, for example using a matcher.

404 pages

Rest parameters also allow you to render custom 404s. Given these routes...

src/routes/
├ marx-brothers/
│ ├ chico/
│ ├ harpo/
│ ├ groucho/
│ └ +error.svelte
└ +error.svelte

...the marx-brothers/+error.svelte file will not be rendered if you visit /marx-brothers/karl, because no route was matched. If you want to render the nested error page, you should create a route that matches any /marx-brothers/* request, and return a 404 from it:

src/routes/
├ marx-brothers/
| ├ [...path]/
│ ├ chico/
│ ├ harpo/
│ ├ groucho/
│ └ +error.svelte
└ +error.svelte

src/routes/marx-brothers/[...path]/+page

import { function error(status: number, body: App.Error): never (+1 overload)Throws an error with a HTTP status code and an optional message.
When called during request handling, this will cause SvelteKit to
return an error response without invoking handleError.
Make sure you’re not catching the thrown error, which would prevent SvelteKit from handling it.
@paramstatus The HTTP status code. Must be in the range 400-599.
@parambody An object that conforms to the App.Error type. If a string is passed, it will be used as the message property.
@throwsHttpError This error instructs SvelteKit to initiate HTTP error handling.
@throwsError If the provided status is invalid (not between 400 and 599).error } from '@sveltejs/kit';

/** @type {import('./$types').PageLoad} */
export function function load(event: any): void@type{import('./$types').PageLoad}load(event: anyevent) {
	function error(status: number, body?: {
    message: string;
} extends App.Error ? App.Error | string | undefined : never): never (+1 overload)Throws an error with a HTTP status code and an optional message.
When called during request handling, this will cause SvelteKit to
return an error response without invoking handleError.
Make sure you’re not catching the thrown error, which would prevent SvelteKit from handling it.
@paramstatus The HTTP status code. Must be in the range 400-599.
@parambody An object that conforms to the App.Error type. If a string is passed, it will be used as the message property.
@throwsHttpError This error instructs SvelteKit to initiate HTTP error handling.
@throwsError If the provided status is invalid (not between 400 and 599).error(404, 'Not Found');
}

import { function error(status: number, body: App.Error): never (+1 overload)Throws an error with a HTTP status code and an optional message.
When called during request handling, this will cause SvelteKit to
return an error response without invoking handleError.
Make sure you’re not catching the thrown error, which would prevent SvelteKit from handling it.
@paramstatus The HTTP status code. Must be in the range 400-599.
@parambody An object that conforms to the App.Error type. If a string is passed, it will be used as the message property.
@throwsHttpError This error instructs SvelteKit to initiate HTTP error handling.
@throwsError If the provided status is invalid (not between 400 and 599).error } from '@sveltejs/kit';
import type { type PageLoad = (event: Kit.LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>) => MaybePromise<void | Record<string, any>>
type PageLoad = (event: Kit.LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>) => MaybePromise<void | Record<string, any>>PageLoad } from './$types';

export const const load: PageLoadload: type PageLoad = (event: Kit.LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>) => MaybePromise<void | Record<string, any>>
type PageLoad = (event: Kit.LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>) => MaybePromise<void | Record<string, any>>PageLoad = (event: Kit.LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>event) => {
	function error(status: number, body?: {
    message: string;
} extends App.Error ? App.Error | string | undefined : never): never (+1 overload)Throws an error with a HTTP status code and an optional message.
When called during request handling, this will cause SvelteKit to
return an error response without invoking handleError.
Make sure you’re not catching the thrown error, which would prevent SvelteKit from handling it.
@paramstatus The HTTP status code. Must be in the range 400-599.
@parambody An object that conforms to the App.Error type. If a string is passed, it will be used as the message property.
@throwsHttpError This error instructs SvelteKit to initiate HTTP error handling.
@throwsError If the provided status is invalid (not between 400 and 599).error(404, 'Not Found');
};

If you don’t handle 404 cases, they will appear in handleError

Optional parameters

A route like [lang]/home contains a parameter named lang which is required. Sometimes it’s beneficial to make these parameters optional, so that in this example both home and en/home point to the same page. You can do that by wrapping the parameter in another bracket pair: [[lang]]/home

Note that an optional route parameter cannot follow a rest parameter ([...rest]/[[optional]]), since parameters are matched ‘greedily’ and the optional parameter would always be unused.

Matching

A route like src/routes/fruits/[page] would match /fruits/apple, but it would also match /fruits/rocketship. We don’t want that. You can ensure that route parameters are well-formed by adding a matcher — which takes the parameter string ("apple" or "rocketship") and returns true if it is valid — to your params directory...

src/params/fruit

/**
 * @param {string} param
 * @return {param is ('apple' | 'orange')}
 * @satisfies {import('@sveltejs/kit').ParamMatcher}
 */
export function function match(param: any): boolean@paramparam 
@return@satisfies{import('@sveltejs/kit').ParamMatcher}match(param: any@paramparam param) {
	return param: any@paramparam param === 'apple' || param: any@paramparam param === 'orange';
}

import type { type ParamMatcher = (param: string) => booleanThe shape of a param matcher. See matching for more info.
ParamMatcher } from '@sveltejs/kit';

export const const match: (param: string) => param is ("apple" | "orange")match = ((param: stringparam: string): param: stringparam is ('apple' | 'orange') => {
	return param: stringparam === 'apple' || param: stringparam === 'orange';
}) satisfies type ParamMatcher = (param: string) => booleanThe shape of a param matcher. See matching for more info.
ParamMatcher;

...and augmenting your routes:

src/routes/fruits/[page=fruit]

If the pathname doesn’t match, SvelteKit will try to match other routes (using the sort order specified below), before eventually returning a 404.

Each module in the params directory corresponds to a matcher, with the exception of *.test.js and *.spec.js files which may be used to unit test your matchers.

Matchers run both on the server and in the browser.

Sorting

It’s possible for multiple routes to match a given path. For example each of these routes would match /foo-abc:

src/routes/[...catchall]/+page.svelte
src/routes/[[a=x]]/+page.svelte
src/routes/[b]/+page.svelte
src/routes/foo-[c]/+page.svelte
src/routes/foo-abc/+page.svelte

SvelteKit needs to know which route is being requested. To do so, it sorts them according to the following rules...

More specific routes are higher priority (e.g. a route with no parameters is more specific than a route with one dynamic parameter, and so on)
Parameters with matchers ([name=type]) are higher priority than those without ([name])
[[optional]] and [...rest] parameters are ignored unless they are the final part of the route, in which case they are treated with lowest priority. In other words x/[[y]]/z is treated equivalently to x/z for the purposes of sorting
Ties are resolved alphabetically

...resulting in this ordering, meaning that /foo-abc will invoke src/routes/foo-abc/+page.svelte, and /foo-def will invoke src/routes/foo-[c]/+page.svelte rather than less specific routes:

src/routes/foo-abc/+page.svelte
src/routes/foo-[c]/+page.svelte
src/routes/[[a=x]]/+page.svelte
src/routes/[b]/+page.svelte
src/routes/[...catchall]/+page.svelte

Encoding

Some characters can’t be used on the filesystem — / on Linux and Mac, \ / : * ? " < > | on Windows. The # and % characters have special meaning in URLs, and the [ ] ( ) characters have special meaning to SvelteKit, so these also can’t be used directly as part of your route.

To use these characters in your routes, you can use hexadecimal escape sequences, which have the format [x+nn] where nn is a hexadecimal character code:

\ — [x+5c]
/ — [x+2f]
: — [x+3a]
* — [x+2a]
? — [x+3f]
" — [x+22]
< — [x+3c]
> — [x+3e]
| — [x+7c]
# — [x+23]
% — [x+25]
[ — [x+5b]
] — [x+5d]
( — [x+28]
) — [x+29]

For example, to create a /smileys/:-) route, you would create a src/routes/smileys/[x+3a]-[x+29]/+page.svelte file.

You can determine the hexadecimal code for a character with JavaScript:

':'.String.charCodeAt(index: number): numberReturns the Unicode value of the character at the specified location.
@paramindex The zero-based index of the desired character. If there is no character at the specified index, NaN is returned.charCodeAt(0).Number.toString(radix?: number): stringReturns a string representation of an object.
@paramradix Specifies a radix for converting numeric values to strings. This value is only used for numbers.toString(16); // '3a', hence '[x+3a]'

You can also use Unicode escape sequences. Generally you won’t need to as you can use the unencoded character directly, but if — for some reason — you can’t have a filename with an emoji in it, for example, then you can use the escaped characters. In other words, these are equivalent:

src/routes/[u+d83e][u+dd2a]/+page.svelte
src/routes/🤪/+page.svelte

The format for a Unicode escape sequence is [u+nnnn] where nnnn is a valid value between 0000 and 10ffff. (Unlike JavaScript string escaping, there’s no need to use surrogate pairs to represent code points above ffff.) To learn more about Unicode encodings, consult Programming with Unicode.

Since TypeScript struggles with directories with a leading . character, you may find it useful to encode these characters when creating e.g. .well-known routes: src/routes/[x+2e]well-known/...

Advanced layouts

By default, the layout hierarchy mirrors the route hierarchy. In some cases, that might not be what you want.

(group)

Perhaps you have some routes that are ‘app’ routes that should have one layout (e.g. /dashboard or /item), and others that are ‘marketing’ routes that should have a different layout (/about or /testimonials). We can group these routes with a directory whose name is wrapped in parentheses — unlike normal directories, (app) and (marketing) do not affect the URL pathname of the routes inside them:

src/routes/
│ (app)/
│ ├ dashboard/
│ ├ item/
│ └ +layout.svelte
│ (marketing)/
│ ├ about/
│ ├ testimonials/
│ └ +layout.svelte
├ admin/
└ +layout.svelte

You can also put a +page directly inside a (group), for example if / should be an (app) or a (marketing) page.

Breaking out of layouts

The root layout applies to every page of your app — if omitted, it defaults to <slot />. If you want some pages to have a different layout hierarchy than the rest, then you can put your entire app inside one or more groups except the routes that should not inherit the common layouts.

In the example above, the /admin route does not inherit either the (app) or (marketing) layouts.

+page@

Pages can break out of the current layout hierarchy on a route-by-route basis. Suppose we have an /item/[id]/embed route inside the (app) group from the previous example:

src/routes/
├ (app)/
│ ├ item/
│ │ ├ [id]/
│ │ │ ├ embed/
│ │ │ │ └ +page.svelte
│ │ │ └ +layout.svelte
│ │ └ +layout.svelte
│ └ +layout.svelte
└ +layout.svelte

Ordinarily, this would inherit the root layout, the (app) layout, the item layout and the [id] layout. We can reset to one of those layouts by appending @ followed by the segment name — or, for the root layout, the empty string. In this example, we can choose from the following options:

+page@[id].svelte - inherits from src/routes/(app)/item/[id]/+layout.svelte
+page@item.svelte - inherits from src/routes/(app)/item/+layout.svelte
+page@(app).svelte - inherits from src/routes/(app)/+layout.svelte
+page@.svelte - inherits from src/routes/+layout.svelte

src/routes/
├ (app)/
│ ├ item/
│ │ ├ [id]/
│ │ │ ├ embed/
│ │ │ │ └ +page@(app).svelte
│ │ │ └ +layout.svelte
│ │ └ +layout.svelte
│ └ +layout.svelte
└ +layout.svelte

+layout@

Like pages, layouts can themselves break out of their parent layout hierarchy, using the same technique. For example, a +layout@.svelte component would reset the hierarchy for all its child routes.

src/routes/
├ (app)/
│ ├ item/
│ │ ├ [id]/
│ │ │ ├ embed/
│ │ │ │ └ +page.svelte  // uses (app)/item/[id]/+layout.svelte
│ │ │ ├ +layout.svelte  // inherits from (app)/item/+layout@.svelte
│ │ │ └ +page.svelte    // uses (app)/item/+layout@.svelte
│ │ └ +layout@.svelte   // inherits from root layout, skipping (app)/+layout.svelte
│ └ +layout.svelte
└ +layout.svelte

When to use layout groups

Not all use cases are suited for layout grouping, nor should you feel compelled to use them. It might be that your use case would result in complex (group) nesting, or that you don’t want to introduce a (group) for a single outlier. It’s perfectly fine to use other means such as composition (reusable load functions or Svelte components) or if-statements to achieve what you want. The following example shows a layout that rewinds to the root layout and reuses components and functions that other layouts can also use:

src/routes/nested/route/+layout@

<script>
	import ReusableLayout from '$lib/ReusableLayout.svelte';
	export let data;
</script>

<ReusableLayout {data}>
	<slot />
</ReusableLayout>

src/routes/nested/route/+layout

import { function reusableLoad(event: import("@sveltejs/kit").LoadEvent): Promise<Record<string, any>>reusableLoad } from '$lib/reusable-load-function';

/** @type {import('./$types').PageLoad} */
export function function load(event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>): MaybePromise<void | Record<string, any>>@type{import('./$types').PageLoad}load(event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>event) {
	// Add additional logic here, if needed
	return function reusableLoad(event: import("@sveltejs/kit").LoadEvent): Promise<Record<string, any>>reusableLoad(event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>event);
}

import { function reusableLoad(event: import("@sveltejs/kit").LoadEvent): Promise<Record<string, any>>reusableLoad } from '$lib/reusable-load-function';
import type { type PageLoad = (event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>) => MaybePromise<void | Record<string, any>>PageLoad } from './$types';

export const const load: PageLoadload: type PageLoad = (event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>) => MaybePromise<void | Record<string, any>>PageLoad = (event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>event) => {
	// Add additional logic here, if needed
	return function reusableLoad(event: import("@sveltejs/kit").LoadEvent): Promise<Record<string, any>>reusableLoad(event: LoadEvent<Record<string, any>, Record<string, any> | null, Record<string, any>, string | null>event);
};