svelte

What is svelte?

Svelte is a modern JavaScript compiler that allows you to write high-performance user interfaces with significantly less boilerplate code than traditional frameworks. It shifts much of the work to compile time, producing highly optimized vanilla JavaScript at the end.

What are svelte's main functionalities?

Reactive Declarations

Svelte allows you to write reactive statements using the $: syntax. When the state changes, the reactive statements automatically update to reflect the new state.

let count = 0;

$: doubled = count * 2;

Component Definition

Components in Svelte are defined using a combination of HTML, CSS, and JavaScript, which are encapsulated within a single file with a .svelte extension.

<script>
  export let name;
</script>

<h1>Hello {name}!</h1>

Store Management

Svelte provides a simple store mechanism to manage global state. The 'writable' store is a basic store that allows reading and writing values reactively.

import { writable } from 'svelte/store';

const count = writable(0);

Transitions and Animations

Svelte makes it easy to add transitions and animations to elements when they enter or leave the DOM.

import { fade } from 'svelte/transition';

<div in:fade={{ delay: 0, duration: 200 }}>Fade In</div>

Bindings

Svelte provides a concise syntax for two-way data binding to HTML elements, allowing for easy synchronization between the DOM and component state.

<script>
  let value = '';
</script>

<input bind:value={value} />

Other packages similar to svelte

react

React is a popular JavaScript library for building user interfaces. It uses a virtual DOM for efficient updates, and it's known for its component-based architecture. Unlike Svelte, React requires a runtime library and often involves more boilerplate code.

vue

Vue is a progressive JavaScript framework used for building UIs and single-page applications. It is similar to Svelte in its component structure and reactivity model but differs in that it uses a virtual DOM and requires a runtime.

angular

Angular is a platform and framework for building single-page client applications using HTML and TypeScript. It is more prescriptive than Svelte, with a complex ecosystem and a steep learning curve, and it includes features like dependency injection and RxJS integration.

preact

Preact is a fast, 3kB alternative to React with the same modern API. It provides a similar component-based architecture but with a smaller footprint. Preact is closer to Svelte in terms of size but still operates with a virtual DOM.

README

What is Svelte?

Svelte is a new way to build web applications. It's a compiler that takes your declarative components and converts them into efficient JavaScript that surgically updates the DOM.

Learn more at the Svelte website, or stop by the Discord chatroom.

Development

Pull requests are encouraged and always welcome. Pick an issue and help us out!

To install and work on Svelte locally:

git clone https://github.com/sveltejs/svelte.git
cd svelte
npm install

Do not use Yarn to install the dependencies, as the specific package versions in package-lock.json are used to build and test Svelte.

Many tests depend on newlines being preserved as <LF>. On Windows, you can ensure this by cloning with:

git -c core.autocrlf=false clone https://github.com/sveltejs/svelte.git

To build the compiler, and all the other modules included in the package:

npm run build

To watch for changes and continually rebuild the package (this is useful if you're using npm link to test out changes in a project locally):

npm run dev

The compiler is written in TypeScript, but don't let that put you off — it's basically just JavaScript with type annotations. You'll pick it up in no time. If you're using an editor other than Visual Studio Code you may need to install a plugin in order to get syntax highlighting and code hints etc.

Running Tests

npm run test

To filter tests, use -g (aka --grep). For example, to only run tests involving transitions:

npm run test -- -g transition

svelte.dev

The source code for https://svelte.dev, including all the documentation, lives in the site directory. The site is built with Sapper. To develop locally:

cd site
npm install && npm run update
npm run dev

License

MIT