mirror of https://github.com/sveltejs/svelte
Docs (#9449)
* rename file * add snippet docs * add note on deprecation * they're not attributes * event docs * prettier * remove unnecessary div * Apply suggestions from code review Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com> * make example less confusing * note breaking props.children change --------- Co-authored-by: Rich Harris <rich.harris@vercel.com> Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>baseballyama-docs/string-event
Rich Harris
8 months ago
committed by
GitHub
parent
e90ded677e
commit
6bba70a2a5
@ -0,0 +1,228 @@
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---
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title: Snippets
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---
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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=)...
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```svelte
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{#each images as image}
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{#if image.href}
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<a href={image.href}>
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<figure>
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<img
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src={image.src}
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alt={image.caption}
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width={image.width}
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height={image.height}
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/>
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<figcaption>{image.caption}</figcaption>
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</figure>
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</a>
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{:else}
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<figure>
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<img
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src={image.src}
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alt={image.caption}
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width={image.width}
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height={image.height}
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/>
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<figcaption>{image.caption}</figcaption>
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</figure>
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{/if}
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{/each}
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```
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...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=):
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```diff
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+{#snippet figure(image)}
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<figure>
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<img
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src={image.src}
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alt={image.caption}
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width={image.width}
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height={image.height}
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/>
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<figcaption>{image.caption}</figcaption>
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</figure>
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+{/snippet}
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{#each images as image}
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{#if image.href}
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<a href={image.href}>
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+ {@render figure(image)}
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</a>
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{:else}
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+ {@render figure(image)}
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{/if}
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{/each}
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```
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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)):
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```svelte
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{#snippet figure({ src, caption, width, height })}
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<figure>
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<img alt={caption} {src} {width} {height} />
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<figcaption>{caption}</figcaption>
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</figure>
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{/snippet}
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```
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## Snippet scope
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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=))...
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```svelte
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<script>
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let { message = `it's great to see you!` } = $props();
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</script>
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{#snippet hello(name)}
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<p>hello {name}! {message}!</p>
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{/snippet}
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{@render hello('alice')}
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{@render hello('bob')}
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```
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...and they are 'visible' to everything in the same lexical scope (i.e. siblings, and children of those siblings):
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```svelte
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<div>
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{#snippet x()}
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{#snippet y()}...{/snippet}
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<!-- this is fine -->
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{@render y()}
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{/snippet}
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<!-- this will error, as `y` is not in scope -->
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{@render y()}
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</div>
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<!-- this will also error, as `x` is not in scope -->
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{@render x()}
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```
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Snippets can reference themselves and each other ([demo](/#H4sIAAAAAAAAE2WPTQqDMBCFrxLiRqH1Zysi7TlqF1YnENBJSGJLCYGeo5tesUeosfYH3c2bee_jjaWMd6BpfrAU6x5oTvdS0g01V-mFPkNnYNRaDKrxGxto5FKCIaeu1kYwFkauwsoUWtZYPh_3W5FMY4U2mb3egL9kIwY0rbhgiO-sDTgjSEqSTvIDs-jiOP7i_MHuFGAL6p9BtiSbOTl0GtzCuihqE87cqtyam6WRGz_vRcsZh5bmRg3gju4Fptq_kzQBAAA=)):
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```svelte
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{#snippet blastoff()}
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<span>🚀</span>
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{/snippet}
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{#snippet countdown(n)}
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{#if n > 0}
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<span>{n}...</span>
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{@render countdown(n - 1)}
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{:else}
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{@render blastoff()}
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{/if}
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{/snippet}
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{@render countdown(10)}
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```
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## Passing snippets to components
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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=)):
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```svelte
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<script>
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import Table from './Table.svelte';
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const fruits = [
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{ name: 'apples', qty: 5, price: 2 },
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{ name: 'bananas', qty: 10, price: 1 },
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{ name: 'cherries', qty: 20, price: 0.5 }
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];
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</script>
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{#snippet header()}
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<th>fruit</th>
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<th>qty</th>
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<th>price</th>
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<th>total</th>
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{/snippet}
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{#snippet row(d)}
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<td>{d.name}</td>
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<td>{d.qty}</td>
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<td>{d.price}</td>
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<td>{d.qty * d.price}</td>
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{/snippet}
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<Table data={fruits} {header} {row} />
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```
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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=)):
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```svelte
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<!-- this is semantically the same as the above -->
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<Table data={fruits}>
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{#snippet header()}
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<th>fruit</th>
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<th>qty</th>
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<th>price</th>
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<th>total</th>
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{/snippet}
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{#snippet row(d)}
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<td>{d.name}</td>
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<td>{d.qty}</td>
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<td>{d.price}</td>
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<td>{d.qty * d.price}</td>
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{/snippet}
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</Table>
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```
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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=)):
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```diff
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<Table data={fruits}>
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- {#snippet header()}
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- <th>fruit</th>
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- <th>qty</th>
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- <th>price</th>
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- <th>total</th>
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- {/snippet}
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+ <th>fruit</th>
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+ <th>qty</th>
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+ <th>price</th>
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+ <th>total</th>
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<!-- ... -->
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</Table>
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```
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```diff
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<script>
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- let { data, header, row } = $props();
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+ let { data, children, row } = $props();
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</script>
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<table>
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- {#if header}
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+ {#if children}
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<thead>
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- <tr>{@render header()}</tr>
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+ <tr>{@render children()}</tr>
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</thead>
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{/if}
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<!-- ... -->
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</table>
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```
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> 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
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## Snippets and slots
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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.
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They continue to work, however, and you can mix and match snippets and slots in your components.
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## Typing snippets
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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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@ -0,0 +1,187 @@
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---
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title: Event handlers
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---
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Event handlers have been given a facelift in Svelte 5. Whereas in Svelte 4 we use the `on:` directive to attach an event listener to an element, in Svelte 5 they are properties like any other:
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```diff
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<script>
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let count = $state(0);
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</script>
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-<button on:click={() => count++}>
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+<button onclick={() => count++}>
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clicks: {count}
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</button>
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```
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Since they're just properties, you can use the normal shorthand syntax...
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```svelte
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<script>
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let count = $state(0);
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function onclick() {
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count++;
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}
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</script>
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<button {onclick}>
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clicks: {count}
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</button>
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```
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...though when using a named event handler function it's usually better to use a more descriptive name.
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Traditional `on:` event handlers will continue to work, but are deprecated in Svelte 5.
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## Component events
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In Svelte 4, components could emit events by creating a dispatcher with [`createEventDispatcher`](https://svelte.dev/docs/svelte#createeventdispatcher).
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|
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This function is deprecated in Svelte 5. Instead, components should accept _callback props_ ([demo](/#H4sIAAAAAAAAE41TS27bMBC9ykBtELu1ZTmAG0C2hPYG3dddyPIwJkKRAjmy4wrad9VFL5BV75cjlKQof5osutCHb968-XCmjRgXaKL0WxvJosIojb7UdTSJ6Fi7g9mjILRnoxpdOmRlSs1rytdyTbyqlSb42lQ1MK0quI1n7hD3brdLR3KPQALDfyBk8N5QQTiaL8bLwbJptKGziRXCoLdaO2tkSVxJ0GiQRmNovSYFtfmij0GDhnf2WLeWq9k5WblymfmsJRM2TtZatSy_EvyYwSDIGYw8lsP9YnzKkXQT5Dv33uJbWhe-ybgvfDooO7-ZT6h9Z3le10utNg2RLVTJUvDyMWt9xV0u8QCbQgilbD09xzd_ZepCQikKY7J1tFGqWkf5y_PvP7Zqa7GcNkXbjO4Nci-3jsDQUaBFTFkITKFN4mQOH3zKnZXry3l5_vXTi5yEZ5x1vqfe39N8gFB_rQx3l5YC40-4DR0VyCiFJJxI1efDgW9pl8I8SW4CskP-sKMriClJU5eZR_eHQQifaFoI_mDDlSgJ9RCPS5yedJZDatxRpri3VJOCVPI0Lu4Th94MpZAu5FCMbxIk8Z259rCtH-iF5FXRsz2cxAsDTOlDobdXXp8f8ci03TgDl_7JDbQQLiOJP0HXw3eLK_x-MRhcey4sPdxPfrgZu7uV2nLGcRulbnq7yWnV3Ub87667RW0h7M4EwuBD5_a21qo2I7ey1xv370QH7y4PPxfz_IobAnR5-DlxXxf0vfsLb_4Z08cEAAA=)):
|
||||
|
||||
```svelte
|
||||
<script>
|
||||
import Pump from './Pump.svelte';
|
||||
|
||||
let size = $state(15);
|
||||
let burst = $state(false);
|
||||
|
||||
function reset() {
|
||||
size = 15;
|
||||
burst = false;
|
||||
}
|
||||
</script>
|
||||
|
||||
<Pump
|
||||
inflate={() => {
|
||||
size += 5;
|
||||
if (size > 75) burst = true;
|
||||
}}
|
||||
deflate={() => {
|
||||
if (size > 0) size -= 5;
|
||||
}}
|
||||
/>
|
||||
|
||||
{#if burst}
|
||||
<button onclick={reset}>new balloon</button>
|
||||
<span class="boom">💥</span>
|
||||
{:else}
|
||||
<span class="balloon" style="scale: {0.01 * size}">
|
||||
🎈
|
||||
</span>
|
||||
{/if}
|
||||
```
|
||||
|
||||
```svelte
|
||||
<script>
|
||||
let { inflate, deflate } = $props();
|
||||
</script>
|
||||
|
||||
<button onclick={inflate}>inflate</button>
|
||||
<button onclick={deflate}>deflate</button>
|
||||
```
|
||||
|
||||
## Bubbling events
|
||||
|
||||
Instead of doing `<button on:click>` to 'forward' the event from the element to the component, the component should accept an `onclick` callback prop:
|
||||
|
||||
```svelte
|
||||
<script>
|
||||
let { onclick, children } = $props();
|
||||
</script>
|
||||
|
||||
<button {onclick}>
|
||||
{@render children()}
|
||||
</button>
|
||||
```
|
||||
|
||||
Note that this also means you can 'spread' event handlers onto the element along with other props:
|
||||
|
||||
```svelte
|
||||
<script>
|
||||
let { children, ...props } = $props();
|
||||
</script>
|
||||
|
||||
<button {...props}>
|
||||
{@render children()}
|
||||
</button>
|
||||
```
|
||||
|
||||
## Event modifiers
|
||||
|
||||
In Svelte 4, you can add event modifiers to handlers:
|
||||
|
||||
```svelte
|
||||
<button on:click|once|preventDefault={handler}>...</button>
|
||||
```
|
||||
|
||||
Modifiers are specific to `on:` and as such do not work with modern event handlers. Adding things like `event.preventDefault()` inside the handler itself is preferable, since all the logic lives in one place rather than being split between handler and modifiers.
|
||||
|
||||
Since event handlers are just functions, you can create your own wrappers as necessary:
|
||||
|
||||
```svelte
|
||||
<script>
|
||||
function once(fn) {
|
||||
return function (event) {
|
||||
if (fn) fn.call(this, event);
|
||||
fn = null;
|
||||
};
|
||||
}
|
||||
|
||||
function preventDefault(fn) {
|
||||
return function (event) {
|
||||
event.preventDefault();
|
||||
fn.call(this, event);
|
||||
};
|
||||
}
|
||||
</script>
|
||||
|
||||
<button onclick={once(preventDefault(handler))}>...</button>
|
||||
```
|
||||
|
||||
There are three modifiers — `capture`, `passive` and `nonpassive` — that can't be expressed as wrapper functions, since they need to be applied when the event handler is bound rather than when it runs.
|
||||
|
||||
For `capture`, we add the modifier to the event name:
|
||||
|
||||
```svelte
|
||||
<button onclickcapture={...}>...</button>
|
||||
```
|
||||
|
||||
Changing the [`passive`](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#using_passive_listeners) option of an event handler, meanwhile, is not something to be done lightly. If you have a use case for it — and you probably don't! - then you will need to use an action to apply the event handler yourself.
|
||||
|
||||
## Multiple event handlers
|
||||
|
||||
In Svelte 4, this is possible:
|
||||
|
||||
```svelte
|
||||
<button on:click={one} on:click={two}>...</button>
|
||||
```
|
||||
|
||||
This is something of an anti-pattern, since it impedes readability (if there are many attributes, it becomes harder to spot that there are two handlers unless they are right next to each other) and implies that the two handlers are independent, when in fact something like `event.stopImmediatePropagation()` inside `one` would prevent `two` from being called.
|
||||
|
||||
Duplicate attributes/properties on elements — which now includes event handlers — are not allowed. Instead, do this:
|
||||
|
||||
```svelte
|
||||
<button
|
||||
onclick={(e) => {
|
||||
one(e);
|
||||
two(e);
|
||||
}}
|
||||
>
|
||||
...
|
||||
</button>
|
||||
```
|
||||
|
||||
## Why the change?
|
||||
|
||||
By deprecating `createEventDispatcher` and the `on:` directive in favour of callback props and normal element properties, we:
|
||||
|
||||
- reduce Svelte's learning curve
|
||||
- remove boilerplate, particularly around `createEventDispatcher`
|
||||
- remove the overhead of creating `CustomEvent` objects for events that may not even have listeners
|
||||
- add the ability to spread event handlers
|
||||
- add the ability to know which event handlers were provided to a component
|
||||
- add the ability to express whether a given event handler is required or optional
|
||||
- increase type safety (previously, it was effectively impossible for Svelte to guarantee that a component didn't emit a particular event)
|
||||
Loading…
Reference in new issue