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Docs #9449

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Nov 14, 2023
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6 changes: 6 additions & 0 deletions .prettierrc
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,12 @@
"useTabs": false,
"tabWidth": 2
}
},
{
"files": ["sites/svelte-5-preview/src/routes/docs/content/**/*.md"],
"options": {
"printWidth": 60
}
}
]
}
Original file line number Diff line number Diff line change
Expand Up @@ -128,7 +128,10 @@ In rare cases, you may need to run code _before_ the DOM updates. For this we ca
messages;

// autoscroll when new messages are added
if (div.offsetHeight + div.scrollTop > div.scrollHeight - 20) {
if (
div.offsetHeight + div.scrollTop >
div.scrollHeight - 20
) {
tick().then(() => {
div.scrollTo(0, div.scrollHeight);
});
Expand Down
228 changes: 228 additions & 0 deletions sites/svelte-5-preview/src/routes/docs/content/01-api/03-snippets.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,228 @@
---
title: Snippets
---

Snippets, and _render tags_, are a way to create reusable chunks of markup inside your components. Instead of writing duplicative code like [this](/#H4sIAAAAAAAAE5VUYW-kIBD9K8Tmsm2yXXRzvQ-s3eR-R-0HqqOQKhAZb9sz_vdDkV1t000vRmHewMx7w2AflbIGG7GnPlK8gYhFv42JthG-m9Gwf6BGcLbVXZuPSGrzVho8ZirDGpDIhldgySN5GpEMez9kaNuckY1ANJZRamRuu2ZnhEZt6a84pvs43mzD4pMsUDDi8DMkQFYCGdkvsJwblFq5uCik9bmJ4JZwUkv1eoknWigX2eGNN6aGXa6bjV8ybP-X7sM36T58SVcrIIV2xVIaA41xeD5kKqWXuqpUJEefOqVuOkL9DfBchGrzWfu0vb-RpTd3o-zBR045Ga3HfuE5BmJpKauuhbPtENlUF2sqR9jqpsPSxWsMrlngyj3VJiyYjJXb1-lMa7IWC-iSk2M5Zzh-SJjShe-siq5kpZRPs55BbSGU5YPyte4vVV_VfFXxVb10dSLf17pS2lM5HnpPxw4Zpv6x-F57p0jI3OKlVnhv5V9wPQrNYQQ9D_f6aGHlC89fq1Z3qmDkJCTCweOGF4VUFSPJvD_DhreVdA0eu8ehJJ5x91dBaBkpWm3ureCFPt3uzRv56d4kdp-2euG38XZ6dsnd3ZmPG9yRBCrzRUvi-MccOdwz3qE-fOZ7AwAhlrtTUx3c76vRhSwlFBHDtoPhefgHX3dM0PkEAAA=)...

```svelte
{#each images as image}
{#if image.href}
<a href={image.href}>
<figure>
<img
src={image.src}
alt={image.caption}
width={image.width}
height={image.height}
/>
<figcaption>{image.caption}</figcaption>
</figure>
</a>
{:else}
<figure>
<img
src={image.src}
alt={image.caption}
width={image.width}
height={image.height}
/>
<figcaption>{image.caption}</figcaption>
</figure>
{/if}
{/each}
```

...you can write [this](/#H4sIAAAAAAAAE5VUYW-bMBD9KxbRlERKY4jWfSA02n5H6QcXDmwVbMs-lnaI_z6D7TTt1moTAnPvzvfenQ_GpBEd2CS_HxPJekjy5IfWyS7BFz0b9id0CM62ajDVjBS2MkLjqZQldoBE9KwFS-7I_YyUOPqlRGuqnKw5orY5pVpUduj3mitUln5LU3pI0_UuBp9FjTwnDr9AHETLMSeHK6xiGoWSLi9yYT034cwSRjohn17zcQPNFTs8s153sK9Uv_Yh0-5_5d7-o9zbD-UqCaRWrllSYZQxLw_HUhb0ta-y4NnJUxfUvc7QuLJSaO0a3oh2MLBZat8u-wsPnXzKQvTtVVF34xK5d69ThFmHEQ4SpzeVRediTG8rjD5vBSeN3E5JyHh6R1DQK9-iml5kjzQUN_lSgVU8DhYLx7wwjSvRkMDvTjiwF4zM1kXZ7DlF1eN3A7IG85e-zRrYEjjm0FkI4Cc7Ripm0pHOChexhcWXzreeZyRMU6Mk3ljxC9w4QH-cQZ_b3T5pjHxk1VNr1CDrnJy5QDh6XLO6FrLNSRb2l9gz0wo3S6m7HErSgLsPGMHkpDZK31jOanXeHPQz-eruLHUP0z6yTbpbrn223V70uMXNSpQSZjpL0y8hcxxpNqA6_ql3BQAxlxvfpQ_uT9GrWjQC6iRHM8D0MP0GQsIi92QEAAA=):

```diff
+{#snippet figure(image)}
<figure>
<img
src={image.src}
alt={image.caption}
width={image.width}
height={image.height}
/>
<figcaption>{image.caption}</figcaption>
</figure>
+{/snippet}

{#each images as image}
{#if image.href}
<a href={image.href}>
+ {@render figure(image)}
</a>
{:else}
+ {@render figure(image)}
{/if}
{/each}
```

A snippet can have at most one parameter. You can destructure it, just like a function argument ([demo](/#H4sIAAAAAAAAE5VTYW-bMBD9KyeiKYlEY4jWfSAk2n5H6QcXDmwVbMs2SzuL_z6DTRqp2rQJ2Ycfd_ced2eXtLxHkxRPLhF0wKRIfiiVpIl9V_PB_MTeoj8bOep6RkpTa67spRKV7dECH2iHBs7wNCOVdcFU1ui6gC2zVpmCEMVrMw4HxaSVhnzLMnLMsm26Ol95Y1kBHr9BDHnHbAHHO6ymynIpfF7LuAncwKgBCj0Xrx_5mMb2jh3f6KB6PNRy2AaXKf1fuY__KPfxj3KlQGikL5aQdpUxm-dTJUryUVdRsvwSqEviX2fIbYzgSvmCt7wbNe4ceMUpRIoUFkkpBBkw7ZfMZXC-BLKSDx3Q3p5djJrA-SR-X4K9DdHT6u-jo-flFlKSO3ThIDcSR6LIKUhGWrN1QGhs16LLbXgbjoe5U1PkozCfzu7uy2WtpfuuUTSo1_9ffPZrJKGLoyuwNxjBv0Q4wmdSR2aFi9jS2Pc-FIrlEKeilcI-GP4LfVtxOM1gyO1XSLp6vtD6tdNyFE0BV8YtngKuaNNw0RWQx_jKDlR33M9E5h-PQhZxfxEt6gIaLdWDYbSR191RvcFXv_LMb7p7obssXZ5Dvt_f9HgzdzZKibOZZ9mXmHkdTTpaefqsd4OIay4_hksd_I0fZMNbjk1SWD3i9Dz9BpdEPu8sBAAA)):

```svelte
{#snippet figure({ src, caption, width, height })}
<figure>
<img alt={caption} {src} {width} {height} />
<figcaption>{caption}</figcaption>
</figure>
{/snippet}
```

## Snippet scope

Snippets can be declared anywhere inside your component. They can reference values declared outside themselves, for example in the `<script>` tag or in `{#each ...}` blocks ([demo](/#H4sIAAAAAAAAE12P0QrCMAxFfyWrwhSEvc8p-h1OcG5RC10bmkyQ0n-3HQPBx3vCPUmCemiDrOpLULYbUdXqTKR2Sj6UA7_RCKbMbvJ9Jg33XpMcW9uKQYEAIzJ3T4QD3LSUDE-PnYA4YET4uOkGMc3W5B3xZrtvbVP9HDas2GqiZHqhMW6Tr9jGbG_oOCMImcUCwrIpFk1FqRyqpRpn0cmjHdAvnrIzuscyq_4nd3dPPD01ukE_NA6qFj9hvMYvGjJADw8BAAA=))...

```svelte
<script>
let { message = `it's great to see you!` } = $props();
</script>

{#snippet hello(name)}
<p>hello {name}! {message}!</p>
{/snippet}

{@render hello('alice')}
{@render hello('bob')}
```

...and they are 'visible' to everything in the same lexical scope (i.e. siblings, and children of those siblings):

```svelte
<div>
{#snippet x()}
{#snippet y()}...{/snippet}

<!-- this is fine -->
{@render y()}
{/snippet}

<!-- this will error, as `y` is not in scope -->
{@render y()}
</div>

<!-- this will also error, as `x` is not in scope -->
{@render x()}
```

Snippets can reference themselves and each other ([demo](/#H4sIAAAAAAAAE2WPTQqDMBCFrxLiRqH1Zysi7TlqF1YnENBJSGJLCYGeo5tesUeosfYH3c2bee_jjaWMd6BpfrAU6x5oTvdS0g01V-mFPkNnYNRaDKrxGxto5FKCIaeu1kYwFkauwsoUWtZYPh_3W5FMY4U2mb3egL9kIwY0rbhgiO-sDTgjSEqSTvIDs-jiOP7i_MHuFGAL6p9BtiSbOTl0GtzCuihqE87cqtyam6WRGz_vRcsZh5bmRg3gju4Fptq_kzQBAAA=)):

```svelte
{#snippet blastoff()}
<span>🚀</span>
{/snippet}

{#snippet countdown(n)}
{#if n > 0}
<span>{n}...</span>
{@render countdown(n - 1)}
{:else}
{@render blastoff()}
{/if}
{/snippet}

{@render countdown(10)}
```

## Passing snippets to components

Within the template, snippets are values just like any other. As such, they can be passed to components as props ([demo](/#H4sIAAAAAAAAE41SwY6bMBD9lRGplKQlYRMpF5ZF7T_0ttmDwSZYJbZrT9pGlv-9g4Fkk-xhxYV5vHlvhjc-aWQnXJK_-kSxo0jy5IcxSZrg2fSF-yM6FFQ7fbJ1jxSuttJguVd7lEejLcJPVnUCGquPMF9nsVoPjfNnohGx1sohMU4SHbzAa4_t0UNvmcOcGUNDzFP4jeccdikYK2v6sIWQ3lErpui5cDdPF_LmkVy3wlp5Vd5e2U_rHYSe_kYjFtl1KeVnTkljBEIrGBd2sYy8AtsyLlBk9DYhJHtTR_UbBDWybkR8NkqHWyOr_y74ZMNLz9f9AoG6ePkOJLMHLBp-xISvcPf11r0YUuMM2Ysfkgngh5XphUYKkJWU_FFz2UjBkxztSYT0cihR4LOn0tGaPrql439N-7Uh0Dl8MVYbt1jeJ1Fg7xDb_Uw2Y18YQqZ_S2U5FH1pS__dCkWMa3C0uR0pfQRTg89kE4bLLLDS_Dxy_Eywuo1TAnPAw4fqY1rvtH3W9w35ZZMgvU3jq8LhedwkguCHRhT_cMU6eVA5dKLB5wGutCWjlTOslupAxxrxceKoD2hzhe2qbmXHF1v1bbOcNCtW_zpYfVI8h5kQ4qY3mueHTlesW2C7TOEO4hcdwzgf3Nc7cZxUKKC4yuNhvIX_MlV_Xk0EAAA=)):

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

const fruits = [
{ name: 'apples', qty: 5, price: 2 },
{ name: 'bananas', qty: 10, price: 1 },
{ name: 'cherries', qty: 20, price: 0.5 }
];
</script>

{#snippet header()}
<th>fruit</th>
<th>qty</th>
<th>price</th>
<th>total</th>
{/snippet}

{#snippet row(d)}
<td>{d.name}</td>
<td>{d.qty}</td>
<td>{d.price}</td>
<td>{d.qty * d.price}</td>
{/snippet}

<Table data={fruits} {header} {row} />
```

As an authoring convenience, snippets declare directly _inside_ a component implicitly become props _on_ the component ([demo](/#H4sIAAAAAAAAE41Sy27bMBD8lYVcwHYrW4kBXxRFaP-htzgHSqQsojLJkuu2BqF_74qUrfhxCHQRh7MzO9z1SSM74ZL8zSeKHUSSJz-MSdIET2Y4uD-iQ0Fnp4-2HpDC1VYaLHdqh_JgtEX4yapOQGP1AebrLJzWsXD-QjQi1lo5JMZRooNXeBuwHXoYLHOYM2OoiXkKv_GUwzYFY2VNFxvo0xtqxRR9F-7z04X8fE-uW2GtnJQ3E_tpvYV-oL9Ti0U2hVJFjMMZslcfW-5DWj9zShojEFrBuLCLZR_9CmzLQCwy-psw8rxBgvkNhhpZd8F8NppE7Stbq_8u-GTKS8_XQ9Keqnl5BZP1AzTYP2bDV7i7_9hLEeda0iocNJeNFDzJ0R5Fn142JzA-uzsdBfLhldPxPdMhIPS0H1-M1cYtlnejwdBDfBXZjHXTFOg4BhuOtvTfrVDEmAZG2ew5ezYV-Ew2fVzVAivNTyPHzwSr29AlMAe8f6g-zuWDts-GusAmdBSkv3P7qnB4GpMEEHwsRPEPV6yTe5VDJxp8iXClLRmtnGG1VHva3oCPHQd9QJsrbFd1Kzu-2Khvz8uzZsXqX3urj4rnMBNCXNUG83zf6Yp1C2yXKdxA_KJjGOfRfb0Vh7MKDShEuV-M9_4_nq6svF4EAAA=)):

```svelte
<!-- this is semantically the same as the above -->
<Table data={fruits}>
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{#snippet header()}
<th>fruit</th>
<th>qty</th>
<th>price</th>
<th>total</th>
{/snippet}

{#snippet row(d)}
<td>{d.name}</td>
<td>{d.qty}</td>
<td>{d.price}</td>
<td>{d.qty * d.price}</td>
{/snippet}
</Table>
```

Any content inside the component tags that is _not_ a snippet declaration implicitly becomes part of the `children` snippet ([demo](/#H4sIAAAAAAAAE41S247aMBD9lVFYCegGsiDxks1G7T_0bdkHJ3aI1cR27aEtsvzvtZ0LZeGhiiJ5js-cmTMemzS8YybJ320iSM-SPPmmVJImeFEhML9Yh8zHRp51HZDC1JorLI_iiLxXUiN8J1XHoNGyh-U2i9F2SFy-epon1lIY9IwzRwNv8B6wI1oIJXNYEqV8E8sUfuIlh0MKSvPaX-zBpZ-oFRH-m7m7l5m8uyfXLdOaX5X3V_bL9gAu0D98i0V2NSWKwQ4lSN7s0LKLbgtsyxgXmT9NiBe-iaP-DYISSTcj4bcLI7hSDEHL3yu6dkPfBdLS0m1o3nk-LW9gX-gBGss9ZsMXuLu32VjZBdfRaelft5eUN5zRJEd9Zi6dlyEy_ncdOm_IxsGlULe8o5qJNFgE5x_9SWmpzGp9N2-MXQxz4c2cOQ-lZWQyF0Jd2q_-mjI9U1fr4FBPE8iuKTbjjRt2sMBK0svIsQtG6jb2CsQAdQ_1x9f5R9tmIS-yPToK-tNkQRQGL6ObCIIdEpH9wQ3p-Enk0LEGXwe4ktoX2hhFai5Ofi0jPnYc9QF1LrDdRK-rvXjerSfNitQ_TlqeBc1hwRi7yY3F81MnK9KtsF2n8Amis44ilA7VtwfWTyr-kaKV-_X4cH8BTOhfRzcEAAA=)):

```diff
<Table data={fruits}>
- {#snippet header()}
- <th>fruit</th>
- <th>qty</th>
- <th>price</th>
- <th>total</th>
- {/snippet}
+ <th>fruit</th>
+ <th>qty</th>
+ <th>price</th>
+ <th>total</th>

<!-- ... -->
</Table>
```

```diff
<script>
- let { data, header, row } = $props();
+ let { data, children, row } = $props();
</script>

<table>
- {#if header}
+ {#if children}
<thead>
- <tr>{@render header()}</tr>
+ <tr>{@render children()}</tr>
</thead>
{/if}

<!-- ... -->
</table>
```

> Note that you cannot have a prop called `children` if you also have content inside the component — for this reason, you should avoid having props with that name

## Snippets and slots

In Svelte 4, content can be passed to components using [slots](https://svelte.dev/docs/special-elements#slot). Snippets are more powerful and flexible, and as such slots are deprecated in Svelte 5.

They continue to work, however, and you can mix and match snippets and slots in your components.

## Typing snippets

Right now, it's not possible to add types for snippets and their parameters. This is something we hope to address before we ship Svelte 5.
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