What are SvelteKit Hooks?
SvelteKit Hooks are special functions introduced by SvelteKit. SvelteKit is a web application framework part of Svelte, which is also an open-source JavaScript framework used for building efficient and fast user interfaces (UIs) for the web. SvelteKit Hooks allow us to manage and control different aspects of our application’s lifecycle. These types of hooks are similar to lifecycle methods in other frameworks like React or Vue.
Note: To learn more about Svelte, check out this course on Introduction to Svelte.
Examples of SvelteKit Hooks
The SvelteKit framework provides several built-in hooks that we can use in our components. Some of the commonly used hooks are listed below:
onMount: This hook is called when the component is added to the DOM (Document Object Model). It comes in handy for setting up event listeners, fetching data, or performing other actions that need to happen after the component is rendered.
beforeUpdate and afterUpdate: These hooks allow us to perform actions before and after a component’s state is updated due to changes in props or data.
onDestroy: This hook is called when a component is removed from the DOM. In addition, it proves to be useful when it comes to cleaning up resources, event listeners, or subscriptions that were set up during the onMount hook.
context: The context hook is used to access the SvelteKit context object, containing information about the current route, params, and other global data.
Code Example
A simple HTML code example with the onMount hook inside the <script> tag (for Javascript code) is shown below to help us understand how SvelteKit Hooks are implemented.
<script>import { onMount } from 'svelte';//importing the onMount Hook from the sveltekit frameworkonMount(() => {console.log('Component mounted!');});//simple message is printed at the end to verify the hook is successfully called</script><h1>Component Mounted!</h1>
The code shown above is present as a part of a SvelteKit application present in the code widget below. Try running it to see it in action!
Note: The code block shown above is present in the
index.htmlfile in the directorysvelte-app/public. This file can be modified to our liking.
# This repo is no longer maintained. Consider using `npm init vite` and selecting the `svelte` option or — if you want a full-fledged app framework — use [SvelteKit](https://kit.svelte.dev), the official application framework for Svelte. --- # svelte app This is a project template for [Svelte](https://svelte.dev) apps. It lives at https://github.com/sveltejs/template. To create a new project based on this template using [degit](https://github.com/Rich-Harris/degit): ```bash npx degit sveltejs/template svelte-app cd svelte-app ``` *Note that you will need to have [Node.js](https://nodejs.org) installed.* ## Get started Install the dependencies... ```bash cd svelte-app npm install ``` ...then start [Rollup](https://rollupjs.org): ```bash npm run dev ``` Navigate to [localhost:8080](http://localhost:8080). You should see your app running. Edit a component file in `src`, save it, and reload the page to see your changes. By default, the server will only respond to requests from localhost. To allow connections from other computers, edit the `sirv` commands in package.json to include the option `--host 0.0.0.0`. If you're using [Visual Studio Code](https://code.visualstudio.com/) we recommend installing the official extension [Svelte for VS Code](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode). If you are using other editors you may need to install a plugin in order to get syntax highlighting and intellisense. ## Building and running in production mode To create an optimised version of the app: ```bash npm run build ``` You can run the newly built app with `npm run start`. This uses [sirv](https://github.com/lukeed/sirv), which is included in your package.json's `dependencies` so that the app will work when you deploy to platforms like [Heroku](https://heroku.com). ## Single-page app mode By default, sirv will only respond to requests that match files in `public`. This is to maximise compatibility with static fileservers, allowing you to deploy your app anywhere. If you're building a single-page app (SPA) with multiple routes, sirv needs to be able to respond to requests for *any* path. You can make it so by editing the `"start"` command in package.json: ```js "start": "sirv public --single" ``` ## Using TypeScript This template comes with a script to set up a TypeScript development environment, you can run it immediately after cloning the template with: ```bash node scripts/setupTypeScript.js ``` Or remove the script via: ```bash rm scripts/setupTypeScript.js ``` If you want to use `baseUrl` or `path` aliases within your `tsconfig`, you need to set up `@rollup/plugin-alias` to tell Rollup to resolve the aliases. For more info, see [this StackOverflow question](https://stackoverflow.com/questions/63427935/setup-tsconfig-path-in-svelte). ## Deploying to the web ### With [Vercel](https://vercel.com) Install `vercel` if you haven't already: ```bash npm install -g vercel ``` Then, from within your project folder: ```bash cd public vercel deploy --name my-project ``` ### With [surge](https://surge.sh/) Install `surge` if you haven't already: ```bash npm install -g surge ``` Then, from within your project folder: ```bash npm run build surge public my-project.surge.sh ```
Advantages
SvelteKit Hooks are known to have numerous advantages. Let’s explore some of these one by one:
- Lifecycle Management: By centralizing common functionality, these hooks provide a structured way to manage component lifecycle actions, making it easier to handle actions like data fetching, setup, and cleanup.
- Readability: They make it clear where different actions are taking place in the component’s lifecycle, improving code readability and maintainability.
- Separation of Concerns: These type of hooks allow us to separate different concerns (e.g., data fetching, UI updates, cleanup) into distinct sections of our component.
- Granular Control: By using these hooks, we have precise control over when actions are executed, as SvelteKit Hooks are specific to certain lifecycle stages.
Disadvantages
Every framework has its pros and cons and SvelteKit Hooks are no different. Listed here are some of the drawbacks of the SvelteKit Hooks:
- Learning Curve: If you are new to the concept of SvelteKit Hooks, it might take time in understanding when and how to use them effectively.
- Potential Complexity: Despite these hooks offering more control, they might lead to more complex code if not used carefully. This especially happens when dealing with components with multiple hooks.
- More Code Required: We may need to write more code to handle different lifecycle actions using hooks, depending on how complex our application is.
- Limited Customisation: Although SvelteKit provides built-in hooks, there might be situations where we need more customized lifecycle behavior that isn’t directly supported by the hooks provided.
Conclusion
To sum up, it’s important to keep in mind that SvelteKit and its features keep on evolving regularly. Hence, it’s recommend to keep on checking the official SvelteKit documentation and resources for the most up-to-date information on hooks and their usage.
Free Resources
