Welcome to Svelte docs. These are for folks who are already familiar with Svelte and want to learn more about the details of how it works.
Welcome to the Svelte reference documentation! This is intended as a resource for people who already have some familiarity with Svelte and want to learn more about using it.
If that's not you (yet), you may prefer to visit the [interactive tutorial](/tutorial) or the [examples](/examples) before consulting this reference.
Don't be shy about asking for help in the [Discord chatroom](https://svelte.dev/chat).
Using an older version of Svelte? Have a look at the [v2 docs](https://v2.svelte.dev).
If that's not you (yet), you may prefer to visit the [interactive tutorial](https://learn.svelte.dev) or the [examples](/examples) before consulting this reference. You can try Svelte online using the [REPL](/repl). Alternatively, if you'd like a more fully-featured environment, you can try Svelte on [StackBlitz](https://sveltekit.new).
## Start a new project
To try Svelte in an interactive online environment you can try [the REPL](https://svelte.dev/repl) or [StackBlitz](https://node.new/svelte).
To create a project locally we recommend using [SvelteKit](https://kit.svelte.dev/), the official application framework from the Svelte team:
We recommend using [SvelteKit](https://kit.svelte.dev/), the official application framework from the Svelte team:
```
npm create svelte@latest myapp
@ -23,22 +17,18 @@ npm install
npm run dev
```
SvelteKit will handle calling [the Svelte compiler](https://www.npmjs.com/package/svelte) to convert your `.svelte` files into `.js` files that create the DOM and `.css` files that style it. It also provides all the other pieces you need to build a web application such as a development server, routing, and deployment. [SvelteKit](https://kit.svelte.dev/) utilizes [Vite](https://vitejs.dev/) to build your code and handle server-side rendering (SSR). There are [plugins for all the major web bundlers](https://sveltesociety.dev/tools#bundling) to handle Svelte compilation, which will output `.js` and `.css` that you can insert into your HTML, but most others won't handle SSR.
SvelteKit will handle calling [the Svelte compiler](https://www.npmjs.com/package/svelte) to convert your `.svelte` files into `.js` files that create the DOM and `.css` files that style it. It also provides all the other pieces you need to build a web application such as a development server, routing, deployment, and SSR support. [SvelteKit](https://kit.svelte.dev/) uses [Vite](https://vitejs.dev/) to build your code.
### Alternatives to SvelteKit
If you don't want to use SvelteKit for some reason, you can also use Svelte with Vite (but without SvelteKit) by running `npm init vite` and selecting the `svelte` option. With this, `npm run build` will generate HTML, JS and CSS files inside the `dist` directory. In most cases, you will probably need to [choose a routing library](/faq#is-there-a-router) as well.
## Differences from SvelteKit
Svelte renders UI components. You can compose these components and render an entire page with just Svelte, but you need more than just Svelte to write an entire app.
SvelteKit provides basic functionality like a [router](https://kit.svelte.dev/glossary#routing) — which updates the UI when a link is clicked — and [server-side rendering (SSR)](https://kit.svelte.dev/glossary#ssr). But beyond that, building an app with all the modern best practices is fiendishly complicated. Those practices include [build optimizations](https://vitejs.dev/guide/features.html#build-optimizations), so that you load only the minimal required code; [offline support](https://kit.svelte.devservice-workers); [preloading](https://kit.svelte.dev/link-options#data-sveltekit-preload-data) pages before the user initiates navigation; [configurable rendering](https://kit.svelte.dev/page-options) that allows you to render different parts of your app on the server with [SSR](https://kit.svelte.dev/glossary#ssr), in the browser [client-side rendering](https://kit.svelte.dev/glossary#csr), or at build-time with [prerendering](https://kit.svelte.dev/glossary#prerendering); and many other things. SvelteKit does all the boring stuff for you so that you can get on with the creative part.
It reflects changes to your code in the browser instantly to provide a lightning-fast and feature-rich development experience by leveraging [Vite](https://vitejs.dev/) with a [Svelte plugin](https://github.com/sveltejs/vite-plugin-svelte) to do [Hot Module Replacement (HMR)](https://github.com/sveltejs/vite-plugin-svelte/blob/main/docs/config.md#hot).
Alternatively, there are [plugins for all the major web bundlers](https://sveltesociety.dev/tools#bundling) to handle Svelte compilation — which will output `.js` and `.css` that you can insert into your HTML — but most others won't handle SSR.
## Editor tooling
The Svelte team maintains a [VS Code extension](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode) and there are integrations with various other [editors](https://sveltesociety.dev/tools#editor-support) and tools as well.
If you're having trouble, get help on [Discord](https://svelte.dev/chat) or [StackOverflow](https://stackoverflow.com/questions/tagged/svelte).
## Getting help
Don't be shy about asking for help in the [Discord chatroom](https://svelte.dev/chat)! You can also find answers on [Stack Overflow](https://stackoverflow.com/questions/tagged/svelte).
@ -101,7 +101,7 @@ Update expressions (`count += 1`) and property assignments (`obj.x = y`) have th
</script>
```
Because Svelte's reactivity is based on assignments, using array methods like `.push()` and `.splice()` won't automatically trigger updates. A subsequent assignment is required to trigger the update. This and more details can also be found in the [tutorial](/tutorial/updating-arrays-and-objects).
Because Svelte's reactivity is based on assignments, using array methods like `.push()` and `.splice()` won't automatically trigger updates. A subsequent assignment is required to trigger the update. This and more details can also be found in the [tutorial](https://learn.svelte.dev/tutorial/updating-arrays-and-objects).
@ -83,13 +83,13 @@ An element or component can have multiple spread attributes, interspersed with r
<Widget{...things}/>
```
_`$$props`_ references all props that are passed to a component, including ones that are not declared with `export`. It is not generally recommended, as it is difficult for Svelte to optimise. But it can be useful in rare cases – for example, when you don't know at compile time what props might be passed to a component.
`$$props` references all props that are passed to a component, including ones that are not declared with `export`. It is not generally recommended, as it is difficult for Svelte to optimise. But it can be useful in rare cases – for example, when you don't know at compile time what props might be passed to a component.
```svelte
<Widget{...$$props}/>
```
_`$$restProps`_ contains only the props which are _not_ declared with `export`. It can be used to pass down other unknown attributes to an element in a component. It shares the same optimisation problems as _`$$props`_, and is likewise not recommended.
`$$restProps` contains only the props which are _not_ declared with `export`. It can be used to pass down other unknown attributes to an element in a component. It shares the same optimisation problems as `$$props`, and is likewise not recommended.
@ -609,7 +609,7 @@ A custom transition function can also return a `tick` function, which is called
{/if}
```
If a transition returns a function instead of a transition object, the function will be called in the next microtask. This allows multiple transitions to coordinate, making [crossfade effects](/tutorial/deferred-transitions) possible.
If a transition returns a function instead of a transition object, the function will be called in the next microtask. This allows multiple transitions to coordinate, making [crossfade effects](https://learn.svelte.dev/tutorial/deferred-transitions) possible.
Transition functions also receive a third argument, `options`, which contains information about the transition.
The `svelte` package exposes [lifecycle functions](/tutorial/onmount) and the [context API](/tutorial/context-api).
The `svelte` package exposes [lifecycle functions](https://learn.svelte.dev/tutorial/onmount) and the [context API](https://learn.svelte.dev/tutorial/context-api).
@ -25,7 +25,7 @@ The `flip` function calculates the start and end position of an element and anim
- a `number`, in milliseconds.
- a function, `distance: number => duration: number`, receiving the distance the element will travel in pixels and returning the duration in milliseconds. This allows you to assign a duration that is relative to the distance travelled by each element.
You can see a full example on the [animations tutorial](/tutorial/animate)
You can see a full example on the [animations tutorial](https://learn.svelte.dev/tutorial/animate).