---
title: .svelte files
---

Components are the building blocks of Svelte applications. They are written into `.svelte` files, using a superset of HTML.

All three sections — script, styles and markup — are optional.

<!-- prettier-ignore -->
```svelte
/// file: MyComponent.svelte
<script module>
	// module-level logic goes here
	// (you will rarely use this)
</script>

<script>
	// instance-level logic goes here
</script>

<!-- markup (zero or more items) goes here -->

<style>
	/* styles go here */
</style>
```

## `<script>`

A `<script>` block contains JavaScript (or TypeScript, when adding the `lang="ts"` attribute) that runs when a component instance is created. Variables declared (or imported) at the top level can be referenced in the component's markup.

In addition to normal JavaScript, you can use _runes_ to declare [component props]($props) and add reactivity to your component. Runes are covered in the next section.

<!-- TODO describe behaviour of `export` -->

## `<script module>`

A `<script>` tag with a `module` attribute runs once when the module first evaluates, rather than for each component instance. Variables declared in this block can be referenced elsewhere in the component, but not vice versa.

```svelte
<script module>
	let total = 0;
</script>

<script>
	total += 1;
	console.log(`instantiated ${total} times`);
</script>
```

You can `export` bindings from this block, and they will become exports of the compiled module. You cannot `export default`, since the default export is the component itself.

> [!LEGACY]
> In Svelte 4, this script tag was created using `<script context="module">`

## `<style>`

CSS inside a `<style>` block will be scoped to that component.

```svelte
<style>
	p {
		/* this will only affect <p> elements in this component */
		color: burlywood;
	}
</style>
```

For more information, head to the section on [styling](scoped-styles).