sapper/site/content/docs/02-routing.md

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Routing

As we've seen, there are two types of route in Sapper — pages, and server routes.

Pages

Pages are Svelte components written in .svelte files. When a user first visits the application, they will be served a server-rendered version of the route in question, plus some JavaScript that 'hydrates' the page and initialises a client-side router. From that point forward, navigating to other pages is handled entirely on the client for a fast, app-like feel.

The filename determines the route. For example, src/routes/index.svelte is the root of your site:

<!-- src/routes/index.svelte -->
<svelte:head>
	<title>Welcome</title>
</svelte:head>

<h1>Hello and welcome to my site!</h1>

A file called either src/routes/about.svelte or src/routes/about/index.svelte would correspond to the /about route:

<!-- src/routes/about.svelte -->
<svelte:head>
	<title>About</title>
</svelte:head>

<h1>About this site</h1>
<p>TODO...</p>

Dynamic parameters are encoded using [brackets]. For example, here's how you could create a page that renders a blog post:

<!-- src/routes/blog/[slug].svelte -->
<script context="module">
	// the (optional) preload function takes a
	// `{ path, params, query }` object and turns it into
	// the data we need to render the page
	export async function preload(page, session) {
		// the `slug` parameter is available because this file
		// is called [slug].svelte
		const { slug } = page.params;

		// `this.fetch` is a wrapper around `fetch` that allows
		// you to make credentialled requests on both
		// server and client
		const res = await this.fetch(`blog/${slug}.json`);
		const article = await res.json();

		return { article };
	}
</script>

<script>
	export let article;
</script>

<svelte:head>
	<title>{article.title}</title>
</svelte:head>

<h1>{article.title}</h1>

<div class='content'>
	{@html article.svelte}
</div>

See the section on preloading for more info about preload and this.fetch

Server routes

Server routes are modules written in .js files that export functions corresponding to HTTP methods. Each function receives HTTP request and response objects as arguments, plus a next function. This is useful for creating a JSON API. For example, here's how you could create an endpoint that served the blog page above:

// routes/blog/[slug].json.js
import db from './_database.js'; // the underscore tells Sapper this isn't a route

export async function get(req, res, next) {
	// the `slug` parameter is available because this file
	// is called [slug].json.js
	const { slug } = req.params;

	const article = await db.get(slug);

	if (article !== null) {
		res.setHeader('Content-Type', 'application/json');
		res.end(JSON.stringify(article));
	} else {
		next();
	}
}

delete is a reserved word in JavaScript. To handle DELETE requests, export a function called del instead.

File naming rules

There are three simple rules for naming the files that define your routes:

• A file called src/routes/about.svelte corresponds to the /about route. A file called src/routes/blog/[slug].svelte corresponds to the /blog/:slug route, in which case params.slug is available to preload
• The file src/routes/index.svelte corresponds to the root of your app. src/routes/about/index.svelte is treated the same as src/routes/about.svelte.
• Files and directories with a leading underscore do not create routes. This allows you to colocate helper modules and components with the routes that depend on them — for example you could have a file called src/routes/_helpers/datetime.js and it would not create a /_helpers/datetime route

Error page

In addition to regular pages, there is a 'special' page that Sapper expects to find — src/routes/_error.svelte. This will be shown when an error occurs while rendering a page.

The error object is made available to the template along with the HTTP status code.

Regexes in routes

You can use a subset of regular expressions to qualify route parameters, by placing them in parentheses after the parameter name.

For example, src/routes/items/[id([0-9]+)].svelte would only match numeric IDs — /items/123 would match, but /items/xyz would not.

Because of technical limitations, the following characters cannot be used: /, \, ?, :, ( and ).