svelte/documentation/docs/02-template-syntax/02-basic-markup.md

---
title: Basic markup
---

- [basically what we have in the Svelte docs today](https://svelte.dev/docs/basic-markup)

## Tags

A lowercase tag, like `<div>`, denotes a regular HTML element. A capitalised tag, such as `<Widget>` or `<Namespace.Widget>`, indicates a _component_.

```svelte
<script>
	import Widget from './Widget.svelte';
</script>

<div>
	<Widget />
</div>
```

## Attributes and props

By default, attributes work exactly like their HTML counterparts.

```svelte
<div class="foo">
	<button disabled>can't touch this</button>
</div>
```

As in HTML, values may be unquoted.

<!-- prettier-ignore -->
```svelte
<input type=checkbox />
```

Attribute values can contain JavaScript expressions.

```svelte
<a href="page/{p}">page {p}</a>
```

Or they can _be_ JavaScript expressions.

```svelte
<button disabled={!clickable}>...</button>
```

Boolean attributes are included on the element if their value is [truthy](https://developer.mozilla.org/en-US/docs/Glossary/Truthy) and excluded if it's [falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy).

All other attributes are included unless their value is [nullish](https://developer.mozilla.org/en-US/docs/Glossary/Nullish) (`null` or `undefined`).

```svelte
<input required={false} placeholder="This input field is not required" />
<div title={null}>This div has no title attribute</div>
```

Quoting a singular expression does not affect how the value is parsed yet, but in Svelte 6 it will:

<!-- prettier-ignore -->
```svelte
<button disabled="{number !== 42}">...</button>
```

When the attribute name and value match (`name={name}`), they can be replaced with `{name}`.

```svelte
<button {disabled}>...</button>
<!-- equivalent to
<button disabled={disabled}>...</button>
-->
```

By convention, values passed to components are referred to as _properties_ or _props_ rather than _attributes_, which are a feature of the DOM.

As with elements, `name={name}` can be replaced with the `{name}` shorthand.

```svelte
<Widget foo={bar} answer={42} text="hello" />
```

_Spread attributes_ allow many attributes or properties to be passed to an element or component at once.

An element or component can have multiple spread attributes, interspersed with regular ones.

```svelte
<Widget {...things} />
```

> The `value` attribute of an `input` element or its children `option` elements must not be set with spread attributes when using `bind:group` or `bind:checked`. Svelte needs to be able to see the element's `value` directly in the markup in these cases so that it can link it to the bound variable.

> Sometimes, the attribute order matters as Svelte sets attributes sequentially in JavaScript. For example, `<input type="range" min="0" max="1" value={0.5} step="0.1"/>`, Svelte will attempt to set the value to `1` (rounding up from 0.5 as the step by default is 1), and then set the step to `0.1`. To fix this, change it to `<input type="range" min="0" max="1" step="0.1" value={0.5}/>`.

> Another example is `<img src="..." loading="lazy" />`. Svelte will set the img `src` before making the img element `loading="lazy"`, which is probably too late. Change this to `<img loading="lazy" src="...">` to make the image lazily loaded.

## Events

Listening to DOM events is possible by adding attributes to the element that start with `on`. For example, to listen to the `click` event, add the `onclick` attribute to a button:

```svelte
<button onclick={() => console.log('clicked')}>click me</button>
```

Event attributes are case sensitive. `onclick` listens to the `click` event, `onClick` listens to the `Click` event, which is different. This ensures you can listen to custom events that have uppercase characters in them.

Because events are just attributes, the same rules as for attributes apply:

- you can use the shorthand form: `<button {onclick}>click me</button>`
- you can spread them: `<button {...thisSpreadContainsEventAttributes}>click me</button>`
- component events are just (callback) properties and don't need a separate concept

### Event delegation

To reduce the memory footprint and increase performance, Svelte uses a technique called event delegation. This means that certain events are only listened to once at the application root, invoking a handler that then traverses the event call path and invokes listeners along the way.

There are a few gotchas you need to be aware of when it comes to event delegation:

- when you dispatch events manually, make sure to set the `{ bubbles: true }` option
- when listening to events programmatically (i.e. not through `<button onclick={...}>` but through `node.addEventListener`), be careful to not call `stopPropagation` or else the delegated event handler won't be reached and handlers won't be invoked. For this reaon it's best to use `on` (which properly handles `stopPropagation`) from `svelte/events` instead of `addEventListener` to make sure the chain of events is preserved

The following events are delegated:

- `beforeinput`
- `click`
- `change`
- `dblclick`
- `contextmenu`
- `focusin`
- `focusout`
- `input`
- `keydown`
- `keyup`
- `mousedown`
- `mousemove`
- `mouseout`
- `mouseover`
- `mouseup`
- `pointerdown`
- `pointermove`
- `pointerout`
- `pointerover`
- `pointerup`
- `touchend`
- `touchmove`
- `touchstart`

## Text expressions

A JavaScript expression can be included as text by surrounding it with curly braces.

```svelte
{expression}
```

Curly braces can be included in a Svelte template by using their [HTML entity](https://developer.mozilla.org/docs/Glossary/Entity) strings: `&lbrace;`, `&lcub;`, or `&#123;` for `{` and `&rbrace;`, `&rcub;`, or `&#125;` for `}`.

If you're using a regular expression (`RegExp`) [literal notation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp#literal_notation_and_constructor), you'll need to wrap it in parentheses.

<!-- prettier-ignore -->
```svelte
<h1>Hello {name}!</h1>
<p>{a} + {b} = {a + b}.</p>

<div>{(/^[A-Za-z ]+$/).test(value) ? x : y}</div>
```

The expression will be stringified and escaped to prevent code injections. If you want to render HTML, use the `{@html}` tag instead.

```svelte
{@html potentiallyUnsafeHtmlString}
```

> Make sure that you either escape the passed string or only populate it with values that are under your control in order to prevent [XSS attacks](https://owasp.org/www-community/attacks/xss/)

## Comments

You can use HTML comments inside components.

```svelte
<!-- this is a comment! --><h1>Hello world</h1>
```

Comments beginning with `svelte-ignore` disable warnings for the next block of markup. Usually, these are accessibility warnings; make sure that you're disabling them for a good reason.

```svelte
<!-- svelte-ignore a11y-autofocus -->
<input bind:value={name} autofocus />
```

You can add a special comment starting with `@component` that will show up when hovering over the component name in other files.

````svelte
<!--
@component
- You can use markdown here.
- You can also use code blocks here.
- Usage:
  ```html
  <Main name="Arethra">
  ```
-->
<script>
	let { name } = $props();
</script>

<main>
	<h1>
		Hello, {name}
	</h1>
</main>
````