SvelteKit

table of content:

• Introduction
• Why SvelteKit
• Create command for SvelteKit application
• Routing
  • Routing case
  • route params
  • route layout
  • route navigation programmatically
  • $app/navigation functions
  • validating params
• Fetch data
  • types of fetch data
  • Throw error from load function

Introduction:

SvelteKit is an application framework for building high performance web application using svelte.

Why SvelteKit:

• File based routing
• pre-rendering
• API routes
• data fetching
• optimized production build system

Create command for SvelteKit application:

npm create svelte@latest learn-sveltekit

cd learn-sveltekit

npm install

npm run dev -- --open

Routing:

• All routes must be placed inside the routes folder within the src folder
• every file that corresponds to a route must be name +pages.svelte.
• svelteKit by default set a not found page. User can edit this.

Routing case:

• imagine user need a page which URL is /about. then just create a folder about. And inside that create +page.svelte to write needed code which shows on about page.
• imagine user need a page which url is /about/company. Do same things for /about part. then create a folder under about folder called company. then in company folder create +page.svelte file.
• imagine user need a page which url is /items/<itemId>. Do same things for /items part. then create a folder under items folder called [itemId]. then in [itemId] folder create +page.svelte file.
• image user need a page which url length can be change frequently. As a example documentation page like /docs/feature1/section2/example1. Here nesting routing can be added frequently. For this svelteKit provide catch all route feature. for the user docs folder create a folder like [...slug]. folder name can be anything. but three dot must be maintained. And get it using $page.params.slug. here user can get the all routes url followed by docs like feature1/section2/example1.
• imagine user need a page which has optional dynamic params. For that just named folder name as [[optionalParam]]

route params:

<script>
    import { page } from '$app/stores';
    const itemId = $page.params.itemId;
</script>

route layout:

• to create a general layout just create a file called +layout.svelte as a sibling of +page.svelte.

route layout group:

• for make a group, create a folder named (groupName). under the folder create what user need to create group layout. that folder doesn't valid in route URL.

breaking out the layout:

• just add suffix of which layout user want in the file name. exp: +page@(auth).svelte (this for show auth layout) or [email protected] (this for root).

route navigation:

just use <a href="/about">about</a> to navigate

route navigation programmatically:

<script>
    import { goto } from '$app/navigation';
    const gotoHome = () => {
        /**
         * @param {String} - path string
         * @param {Object} - { replaceState: true | false }
         */
        goto('/', { replaceState: true });
    };
</script>

<button on:click="{gotoHome}">goto home</button>

$app/navigation functions:

• goto - navigate dynamically
• beforeNavigate - a callback function which call before navigation initiate
• afterNavigate - a callback function which call after coming back to that page by clicking back button of a browser.

validating params:

• create a folder called params in the src folder
• then create a js file at any name.
• now create a function as named match and export it.
• then rename the dynamic folder to [paramKey=fileName] which need to validate. for example: dynamic folder name is [itemId]. and the validate file name is integer.js. So renamed folder name should be [itemId=integer]

fetch data:

In SvelteKit there is builtin system to fetch data. the process is given bellow.

• create a file named +page.js in parallel with which page data need to fetch.
• create a function named load. function body is given bellow.

export const load = async (loadEvent) => {
    const { fetch } = loadEvent;
    const title = 'users list';
    const response = await fetch('https://jsonplaceholder.typicode.com/users');
    const users = await response.json();
    return { title, users };
};

• Now call it from +page.svelte. calling process is given bellow

<script>
    export let data;
    const users = data.users;
</script>

types of fetch data:

• client side (Universal)
• server side (server load)

Difference between client and server load:

client side	server side
run in both	only run in server

client side:

// +page.js
export const load = async (loadEvent) => {
    /**
     * @property{fetch} - fetch function from the loadEvent
     * @property{params} - params object from the loadEvent
     * @property{url} - url object from the loadEvent
     * @property{route} - route object from the loadEvent
     */
    const { fetch, params, url, route } = loadEvent;
    // call api
};

server side:

// +page.server.js
export const load = async (serverLoadEvent) => {
    /**
     * @property{fetch} - fetch function from the serverLoadEvent
     * @property{params} - params object from the serverLoadEvent
     * @property{url} - url object from the serverLoadEvent
     * @property{route} - route object from the serverLoadEvent
     */
    const { fetch, params, url, route } = serverLoadEvent;
    // call api
};

Throw error from load function:

When api fetching gonna fail or manually errors need to handle, then SvelteKit provide a feature to throw error. By throwing error shows the default error page. Otherwise user need to create a +error.svelte page as a sibling of data visualizing page. The process is given bellow.

// +page.svelte
export const load = async (loadEvent) => {
  const { fetch } = loadEvent;
  const response = await fetch(`https://jsonplaceholder.typicode.com/users`);
  if (response.statusText === "OK") {
    const user = await response.json();
    return { user };
  }
  else {
    throw error(404, "User not found");
  }
}

For custom error page

<!-- +error.svelte -->
<script>
  import {page} from "$app/stores";
</script>

<div>
  <h1>
    {$page.status}: {$page.error.message}
  </h1>
</div>