|
|
---
|
|
|
title: 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>
|
|
|
```
|
|
|
|
|
|
An expression might include characters that would cause syntax highlighting to fail in regular HTML, so quoting the value is permitted. The quotes do not affect how the value is parsed:
|
|
|
|
|
|
<!-- 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} />
|
|
|
```
|
|
|
|
|
|
`$$props` references all props that are passed to a component, including ones that are not declared with `export`. Using `$$props` will not perform as well as references to a specific prop because changes to any prop will cause Svelte to recheck all usages of `$$props`. But it can be useful in some cases – for example, when you don't know at compile time what props might be passed to a component.
|
|
|
|
|
|
```svelte
|
|
|
<Widget {...$$props} />
|
|
|
```
|
|
|
|
|
|
`$$restProps` contains only the props which are _not_ declared with `export`. It can be used to pass down other unknown attributes to an element in a component. It shares the same performance characteristics compared to specific property access as `$$props`.
|
|
|
|
|
|
```svelte
|
|
|
<input {...$$restProps} />
|
|
|
```
|
|
|
|
|
|
> 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.
|
|
|
|
|
|
## 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: `{`, `{`, or `{` for `{` and `}`, `}`, or `}` 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>
|
|
|
```
|
|
|
|
|
|
## 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 />
|
|
|
```
|
