* Ignore whitespace in `{#each}` blocks when containing elements with `animate:` ([#5477](https://github.com/sveltejs/svelte/pull/5477))
* Throw compiler error when variable in `context="instance"` collides with import in `context="module"` ([#7090](https://github.com/sveltejs/svelte/issues/7090))
* Fix compiler crash when `{@const}` contains arrow functions ([#7134](https://github.com/sveltejs/svelte/issues/7134))
## 3.46.2
* Export `FlipParams` interface from `svelte/animate` ([#7103](https://github.com/sveltejs/svelte/issues/7103))
* Fix style manager conflicts when using multiple Svelte instances ([#7026](https://github.com/sveltejs/svelte/issues/7026))
* Fix hydration when using `{@html}` ([#7115](https://github.com/sveltejs/svelte/issues/7115))
## 3.45.0
* Fix non-boolean attribute rendering in SSR to render truthy values as-is ([#6121](https://github.com/sveltejs/svelte/issues/6121))
* Fix binding to a member expression also invalidating the member property ([#6921](https://github.com/sveltejs/svelte/issues/6921))
* Fix default values in `{#each}`/etc. destructurings not being considered references for the purposes of compiler warnings ([#6964](https://github.com/sveltejs/svelte/issues/6964))
* Fix `{:else if}` value incorrectly being cached ([#7043](https://github.com/sveltejs/svelte/pull/7043))
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
@ -12,7 +12,7 @@ Because of that, getting started with it can be a little bit confusing at first.
## 1. Use the REPL
The [Svelte REPL](repl) is the easiest way to begin. You can choose from a list of examples to get you started, and tweak them until they do what you want.
The [Svelte REPL](/repl) is the easiest way to begin. You can choose from a list of examples to get you started, and tweak them until they do what you want.
<aside><p>You'll need to have <ahref="https://nodejs.org/">Node.js</a> installed, and know how to use the terminal</p></aside>
@ -52,7 +52,7 @@ npm run dev
This will create a new project in the `my-svelte-project` directory, install its dependencies, and start a server on http://localhost:5000.
You can find more information about using TypeScript [here](blog/svelte-and-typescript).
You can find more information about using TypeScript [here](/blog/svelte-and-typescript).
Once you've tinkered a bit and understood how everything fits together, you can fork [sveltejs/template](https://github.com/sveltejs/template) and start doing this instead:
@ -28,7 +28,7 @@ The consequence of all this is the **append-only stylesheet**. There's no way of
The idea behind SFCs is simple: you write your components in an HTML file that (optionally) contains a `<style>` and `<script>` attribute describing the component's styles and behaviour. Svelte, Ractive, Vue and Polymer all follow this basic pattern.
<aside>
<p><ahref="blog/frameworks-without-the-framework">Read the introductory blog post</a> if you're new to Svelte. Or <ahref="https://twitter.com/padolsey/status/899717303234908160">read</a><ahref="https://twitter.com/sveltejs/status/901818357644701696">the</a><ahref="https://twitter.com/sveltejs/status/901818106309476352">testimonials</a>.</p>
<p><ahref="/blog/frameworks-without-the-framework">Read the introductory blog post</a> if you're new to Svelte. Or <ahref="https://twitter.com/padolsey/status/899717303234908160">read</a><ahref="https://twitter.com/sveltejs/status/901818357644701696">the</a><ahref="https://twitter.com/sveltejs/status/901818106309476352">testimonials</a>.</p>
</aside>
(For the rest of this article we'll be using Svelte, obviously. But if the idea of using a template language makes you shudder — your fears are misplaced, but that's a topic for another day — then just use Vue which lets you use JSX in your SFCs.)
[Svelte introduced a radical idea](blog/frameworks-without-the-framework): what if your UI framework wasn't a framework at all, but a compiler that turned your components into standalone JavaScript modules? Instead of using a library like React or Vue, which knows nothing about your app and must therefore be a one-size-fits-all solution, we can ship highly-optimised vanilla JavaScript. Just the code your app needs, and without the memory and performance overhead of solutions based on a virtual DOM.
[Svelte introduced a radical idea](/blog/frameworks-without-the-framework): what if your UI framework wasn't a framework at all, but a compiler that turned your components into standalone JavaScript modules? Instead of using a library like React or Vue, which knows nothing about your app and must therefore be a one-size-fits-all solution, we can ship highly-optimised vanilla JavaScript. Just the code your app needs, and without the memory and performance overhead of solutions based on a virtual DOM.
The JavaScript world is [moving towards this model](https://tomdale.net/2017/09/compilers-are-the-new-frameworks/). [Stencil](https://stenciljs.com), a Svelte-inspired framework from the Ionic team, compiles to web components. [Glimmer](https://glimmerjs.com) *doesn't* compile to standalone JavaScript (the pros and cons of which deserve a separate blog post), but the team is doing some fascinating research around compiling templates to bytecode. (React is [getting in on the action](https://twitter.com/trueadm/status/944908776896978946), though their current research focuses on optimising your JSX app code, which is arguably more similar to the ahead-of-time optimisations that Angular, Ractive and Vue have been doing for a few years.)
@ -66,7 +66,7 @@ But size is only part of the story. Svelte apps are also extremely performant an
The biggest drawback for many developers evaluating Sapper would be 'but I like React, and I already know how to use it', which is fair.
If you're in that camp, I'd invite you to at least try alternative frameworks. You might be pleasantly surprised! The [Sapper RealWorld](https://github.com/sveltejs/realworld) implementation totals 1,201 lines of source code, compared to 2,377 for the reference implementation, because you're able to express concepts very concisely using Svelte's template syntax (which [takes all of five minutes to master](https://v2.svelte.dev/guide#template-syntax)). You get [scoped CSS](blog/the-zen-of-just-writing-css), with unused style removal and minification built-in, and you can use preprocessors like LESS if you want. You no longer need to use Babel. SSR is ridiculously fast, because it's just string concatenation. And we recently introduced [svelte/store](https://v2.svelte.dev/guide#state-management), a tiny global store that synchronises state across your component hierarchy with zero boilerplate. The worst that can happen is that you'll end up feeling vindicated!
If you're in that camp, I'd invite you to at least try alternative frameworks. You might be pleasantly surprised! The [Sapper RealWorld](https://github.com/sveltejs/realworld) implementation totals 1,201 lines of source code, compared to 2,377 for the reference implementation, because you're able to express concepts very concisely using Svelte's template syntax (which [takes all of five minutes to master](https://v2.svelte.dev/guide#template-syntax)). You get [scoped CSS](/blog/the-zen-of-just-writing-css), with unused style removal and minification built-in, and you can use preprocessors like LESS if you want. You no longer need to use Babel. SSR is ridiculously fast, because it's just string concatenation. And we recently introduced [svelte/store](https://v2.svelte.dev/guide#state-management), a tiny global store that synchronises state across your component hierarchy with zero boilerplate. The worst that can happen is that you'll end up feeling vindicated!
But there are trade-offs nonetheless. Some people have a pathological aversion to any form of 'template language', and maybe that applies to you. JSX proponents will clobber you with the 'it's just JavaScript' mantra, and therein lies React's greatest strength, which is that it is infinitely flexible. That flexibility comes with its own set of trade-offs, but we're not here to discuss those.
@ -47,7 +47,7 @@ Misunderstood claims about virtual DOM performance date back to the launch of Re
> This is actually extremely fast, primarily because most DOM operations tend to be slow. There's been a lot of performance work on the DOM, but most DOM operations tend to drop frames.
<figure>
<imgalt="Pete Hunt at JSConfEU 2013"src="media/rethinking-best-practices.jpg">
<imgalt="Pete Hunt at JSConfEU 2013"src="/media/rethinking-best-practices.jpg">
<figcaption>Screenshot from <ahref="https://www.youtube.com/watch?v=x7cQ3mrcKaY">Rethinking Best Practices</a> at JSConfEU 2013</figcaption>
@ -159,6 +159,6 @@ In Vue, meanwhile, we have a default export with a `data` function that returns
## Death to boilerplate
These are just some of the ways that Svelte helps you build user interfaces with a minimum of fuss. There are plenty of others — for example, [reactive declarations](tutorial/reactive-declarations) essentially do the work of React's `useMemo`, `useCallback` and `useEffect` without the boilerplate (or indeed the garbage collection overhead of creating inline functions and arrays on each state change).
These are just some of the ways that Svelte helps you build user interfaces with a minimum of fuss. There are plenty of others — for example, [reactive declarations](/tutorial/reactive-declarations) essentially do the work of React's `useMemo`, `useCallback` and `useEffect` without the boilerplate (or indeed the garbage collection overhead of creating inline functions and arrays on each state change).
How? By choosing a different set of constraints. Because [Svelte is a compiler](blog/frameworks-without-the-framework), we're not bound to the peculiarities of JavaScript: we can *design* a component authoring experience, rather than having to fit it around the semantics of the language. Paradoxically, this results in *more* idiomatic code — for example using variables naturally rather than via proxies or hooks — while delivering significantly more performant apps.
How? By choosing a different set of constraints. Because [Svelte is a compiler](/blog/frameworks-without-the-framework), we're not bound to the peculiarities of JavaScript: we can *design* a component authoring experience, rather than having to fit it around the semantics of the language. Paradoxically, this results in *more* idiomatic code — for example using variables naturally rather than via proxies or hooks — while delivering significantly more performant apps.
@ -12,13 +12,13 @@ We think you're going to love it.
## What is Svelte?
Svelte is a component framework —like React or Vue — but with an important difference. Traditional frameworks allow you to write *declarative* state-driven code, but there's a penalty: the browser must do extra work to convert those declarative structures into DOM operations, using techniques like [virtual DOM diffing](blog/virtual-dom-is-pure-overhead) that eat into your frame budget and tax the garbage collector.
Svelte is a component framework —like React or Vue — but with an important difference. Traditional frameworks allow you to write *declarative* state-driven code, but there's a penalty: the browser must do extra work to convert those declarative structures into DOM operations, using techniques like [virtual DOM diffing](/blog/virtual-dom-is-pure-overhead) that eat into your frame budget and tax the garbage collector.
Instead, Svelte runs at *build time*, converting your components into highly efficient *imperative* code that surgically updates the DOM. As a result, you're able to write ambitious applications with excellent performance characteristics.
The first version of Svelte was all about [testing a hypothesis](blog/frameworks-without-the-framework) — that a purpose-built compiler could generate rock-solid code that delivered a great user experience. The second was a small upgrade that tidied things up a bit.
The first version of Svelte was all about [testing a hypothesis](/blog/frameworks-without-the-framework) — that a purpose-built compiler could generate rock-solid code that delivered a great user experience. The second was a small upgrade that tidied things up a bit.
Version 3 is a significant overhaul. Our focus for the last five or six months has been on delivering an outstanding *developer* experience. It's now possible to write components with [significantly less boilerplate](blog/write-less-code) than you'll find elsewhere. Try the brand new [tutorial](tutorial) and see what we mean —if you're familiar with other frameworks we think you'll be pleasantly surprised.
Version 3 is a significant overhaul. Our focus for the last five or six months has been on delivering an outstanding *developer* experience. It's now possible to write components with [significantly less boilerplate](/blog/write-less-code) than you'll find elsewhere. Try the brand new [tutorial](/tutorial) and see what we mean —if you're familiar with other frameworks we think you'll be pleasantly surprised.
To make that possible we first needed to rethink the concept at the heart of modern UI frameworks: reactivity.
@ -94,4 +94,4 @@ We don't take this lightly: hopefully once you've experienced Svelte 3 you'll un
As grueling as this release has been, we're nowhere near finished. We have a ton of ideas for generating smarter, more compact code, and a long feature wish-list. [Sapper](https://sapper.svelte.dev), our Next.js-style app framework, is still in the middle of being updated to use Svelte 3. The [Svelte Native](https://svelte-native.technology/) community project, which allows you to write Android and iOS apps in Svelte, is making solid progress but deserves more complete support from core. We don't yet have the bounty of editor extensions, syntax highlighters, component kits, devtools and so on that other frameworks have, and we should fix that. We *really* want to add first-class TypeScript support.
But in the meantime we think Svelte 3 is the best way to build web apps yet. Take an hour to go through the [tutorial](tutorial) and we hope to convince you of the same. Either way, we'd love to see you in our [Discord chatroom](chat) and on [GitHub](https://github.com/sveltejs/svelte) — everyone is welcome, especially you.
But in the meantime we think Svelte 3 is the best way to build web apps yet. Take an hour to go through the [tutorial](/tutorial) and we hope to convince you of the same. Either way, we'd love to see you in our [Discord chatroom](https://svelte.dev/chat) and on [GitHub](https://github.com/sveltejs/svelte) — everyone is welcome, especially you.
@ -10,7 +10,7 @@ It's been by far the most requested feature for a while, and it's finally here:
We think it'll give you a much nicer development experience — one that also scales beautifully to larger Svelte code bases — regardless of whether you use TypeScript or JavaScript.
<figure>
<imgalt="Screenshot of TypeScript in Svelte"src="media/svelte-ts.png">
<imgalt="Screenshot of TypeScript in Svelte"src="/media/svelte-ts.png">
<figcaption>Image of TypeScript + Svelte in VS Code (theme is <ahref="https://marketplace.visualstudio.com/items?itemName=karyfoundation.theme-karyfoundation-themes">Kary Pro</a>.)</figcaption>
@ -10,7 +10,7 @@ Lots to cover this month with releases from across the Svelte ecosystem. Most im
Let's dive into the news 🐬
## What's new in `sveltejs/svelte`
* SSR store handling has been reworked to subscribe and unsubscribe as in DOM mode. SSR stores should work much more consistently now (**3.31.2**, see [custom stores](https://svelte.dev/examples#custom-stores) and [Server-side component API ](https://svelte.dev/docs#run-time-server-side-component-api))
* SSR store handling has been reworked to subscribe and unsubscribe as in DOM mode. SSR stores should work much more consistently now (**3.31.2**, see [custom stores](https://svelte.dev/examples/custom-stores) and [Server-side component API ](https://svelte.dev/docs#run-time-server-side-component-api))
* Multiple instances of the same action are now allowed on an element (**3.32.0**, [example](https://svelte.dev/repl/01a14375951749dab9579cb6860eccde?version=3.32.0))
* The new `foreign` namespace should make it easier for alternative compile targets (like Svelte Native and SvelteGUI) by disabling certain HTML5-specific behaviour and checks (**3.32.0**, [more info](https://github.com/sveltejs/svelte/pull/5652))
* Support for inline comment sourcemaps in code from preprocessors (**3.32.0**)
description: "Faster builds with SvelteKit and a much anticipated REPL feature"
author: Daniel Sandoval
authorURL: https://desandoval.net
---
Happy new year, Svelte Community! Lots to share this month across Svelte, SvelteKit, Language Tools and the Showcase. Thanks to everyone who made 2021 a great year to use Svelte. Looking forward to the next one 🚀
## What's new in SvelteKit
- `@sveltejs/adapter-static` for SvelteKit now has a `precompress` option to make brotli compression of assets and pages easier to do out of the box ([#3079](https://github.com/sveltejs/kit/pull/3079))
- Concurrency mode in SvelteKit will now prerender pages in parallel ([#3120](https://github.com/sveltejs/kit/pull/3120)). It is enabled by default in `1.0.0-next.205` and later
- CSS is now automatically included before JS for improved page performance ([d13efe](https://github.com/sveltejs/kit/commit/d138efe21692f5925f1e89afc0a33f42d6a1a711))
- A new config option adds the ability to disable service worker registration to do your own custom registration ([#2988](https://github.com/sveltejs/kit/pull/2988))
- SSR route-splitting is here - breaking monolithic builds into smaller pieces for improved startup and routing performance ([#2931](https://github.com/sveltejs/kit/pull/2931))
- `request.origin/path/query` is now `request.url` - simplifying the config and page `load` functions ([#3126](https://github.com/sveltejs/kit/pull/3126))
- After the [update to Vite 2.7](https://github.com/sveltejs/kit/pull/3018), SvelteKit users are [reporting significant performance improvements](https://www.reddit.com/r/sveltejs/comments/rljhfc/sveltekit_massive_compiler_improvement_by/) and loading third-parties libraries in SSR has also been greatly improved
- SvelteKit server will now automatically restart when the config files is changed ([vite-plugin-svelte#237](https://github.com/sveltejs/vite-plugin-svelte/pull/237))
## Other new bits from `svelte/*`
- [Svelte 3.44.3](https://github.com/sveltejs/svelte/blob/master/CHANGELOG.md#3443) is out with a few bug fixes in the binding and loop code
- Svelte Language Tools has introduced support for the then/catch shorthands from Svelte 3.41 and TypeScript's "go to" functionality ([105.8.0 and later](https://github.com/sveltejs/language-tools/releases/tag/extensions-105.8.0))
- The Svelte REPL got a nice upgrade as well - letting you delete saved REPLs. Try it out by logging in at [svelte.dev/apps](https://svelte.dev/apps)
---
## Community Showcase
**Apps & Sites**
- [Discover Twitter Spaces](https://github.com/navneetsharmaui/discover-twitter-spaces) is a tool that helps you find the Twitter Spaces
- [Unnwhiteboard](https://github.com/AviKKi/unnwhiteboard) is a job board for companies (or teams) that don't do "whiteboard" interviews
- [Secret Santa](https://gitlab.com/arturoguzman/secret-santa-sveltekit) is a gift giving coordination app developed with easiness in mind
- [LogSnag](https://logsnag.com/) notifies you of your projects' events and provides you with a timeline to keep track of anything important that happens
- [Version 0.2 of Tangent](http://tangentnotes.com/Download), a Svelte-based note writing app, is now in beta
- [Intl Explorer](https://github.com/jesperorb/intl-explorer) is a tool for viewing output for all possible formatters for Intl
A lot of work this month has gone into migrating the Svelte main website and Svelte REPL to live in the https://github.com/sveltejs/sites repository - including a brand new homepage for [svelte.dev](https://svelte.dev/). Thanks to all the contributors who made this possible!
If you're looking for a fun SvelteKit project to work on, [you can contribute to the Svelte Society site rewrite](https://github.com/svelte-society/sveltesociety-2021/issues) 💅
**Learning and Listening**
_To Read_
- [Mutating Query Params in SvelteKit Without Page Reloads or Navigations](https://dev.to/mohamadharith/mutating-query-params-in-sveltekit-without-page-reloads-or-navigations-2i2b) by Mohamad Harith
- [Svelte for Reactaholics : A guide for React developers](https://www.100ms.live/blog/svelte-guide-for-react-developers) by Puru Vijay
- [Svelte's lifecycle methods can be used anywhere](https://geoffrich.net/posts/svelte-lifecycle-examples/) and [The many meanings of $ in Svelte](https://geoffrich.net/posts/svelte-$-meanings/) by Geoff Rich
- [Vercel and Svelte: A Perfect Match for Web Developers](https://thenewstack.io/vercel-and-svelte-a-perfect-match-for-web-developers/) by Darryl K. Taft
- [User-defined TailwindCSS Color Scheme with Svelte Stores](https://blog.dayslice.io/user-defined-tailwindcss-color-scheme-with-svelte-stores-ad80ca2cf038) by jeremy zaborowski
- [Ionic 6 + Svelte 🚀](https://medium.com/@raymondboswel/ionic-6-svelte-ae904caa82df) by Raymond Boswel
- [What happened in #Svelte language tools this year](https://twitter.com/dummdidumm_/status/1474158105395179525?t=ytj2K2Q52iD5-lNyLnQaAQ&s=19) by Simon H
_To Watch_
- [The Future of Svelte (Interview with Rich Harris)](https://www.youtube.com/watch?v=uQntFkK8Z54) by Lee Robinson, Director of Developer Relations at Vercel
- [Svelte is becoming the go-to framework](https://www.youtube.com/watch?v=fo6BKY2xR2w&t=1834s) for Obsidian plugin developers
- [Sveltekit WordPress Headless Blog](https://www.youtube.com/watch?v=c0UDVgjPxFw) by WebJeda
- [Getting started with SvelteKit](https://www.youtube.com/watch?v=i2suPKMPUFA) by Lihau Tan
- [Deploy a full-stack SvelteKit app on Cloudflare Pages](https://www.youtube.com/watch?v=Wc1_U6Dy5Tw) by 1nf
_To Listen To_
- [Syntax podcast: How To Do Things In Svelte](https://podcasts.apple.com/ca/podcast/how-to-do-things-in-svelte/id1253186678?i=1000544796072)
- [JS Party #205: So much Sveltey goodness (w/ Rich Harris)](https://changelog.com/jsparty/205)
**Libraries, Tools & Components**
- [svelte-headlessui](https://github.com/rgossiaux/svelte-headlessui) is an unofficial, complete Svelte port of the Headless UI component library
- [svelte-forms v2](https://chainlist.github.io/svelte-forms/) has been released - the author is [looking for feedback](https://www.reddit.com/r/sveltejs/comments/r6354j/svelteforms_v2_has_been_released/)
- [Percival](https://github.com/ekzhang/percival) is a declarative data query and visualization language
- [Svelte FlatList](https://github.com/snuffyDev/svelte-flatlist) is a mobile-friendly, simple, and customizable draggable menu
- [svelte-keyed](https://github.com/bryanmylee/svelte-keyed) is a writable derived store for objects and arrays
- [Svemix](https://github.com/svemix/svemix) is Remix for Svelte - providing server scripts inside your Svelte components/routes, which will be transformed into endpoints
Want to add something to the showcase? Need help bringing your next idea to life in Svelte? Join us on [Reddit](https://www.reddit.com/r/sveltejs/) or [Discord](https://discord.com/invite/yy75DKs).
description: "Scaling the team, building partnerships, and growing the community"
author: Ben McCann
authorURL: https://www.benmccann.com/
---
[Svelte](/) is a frontend framework for building fast reactive web apps with less code. If you’re new here, [check out the tutorial](/tutorial) or [examples](/examples) to get a feel for it.
Svelte was [launched 5 years ago](https://news.ycombinator.com/item?id=13069841) and has [come a long way in the time since](https://www.youtube.com/watch?v=YeY5M29-WcY). In 2021, as usage more than doubled, it was voted the [most loved](https://insights.stackoverflow.com/survey/2021#section-most-loved-dreaded-and-wanted-web-frameworks) framework with the [most satisfied](https://2020.stateofjs.com/en-US/technologies/front-end-frameworks/) developers in a pair of surveys. Alongside high-profile companies like The New York Times, Apple, Spotify, Square, Rakuten, Bloomberg, Reuters, Ikea, Brave, and countless others, Svelte is used to power everything from hobby projects to embedded systems interfaces.
To help developers build fully-featured applications with Svelte without worrying about the hard parts, we’ve been developing the [SvelteKit](https://kit.svelte.dev/) application framework. We’re moving quickly towards a [stable 1.0 release](https://github.com/sveltejs/kit/issues?q=is%3Aopen+is%3Aissue+milestone%3A1.0) with the help of early adopters who have already downloaded SvelteKit almost one million times.
## Scaling the team
Rich Harris, Svelte’s creator, has [joined Vercel to work on Svelte full-time](https://vercel.com/blog/vercel-welcomes-rich-harris-creator-of-svelte). We’re incredibly excited to have Rich’s level of involvement in Svelte increase even more and have him steward Svelte into the future.
Svelte has been made possible by the work of a large, dedicated community. Svelte has added numerous core maintainers over the course of the pandemic, including three this past week. In alphabetical order:
- [benmccann](https://github.com/benmccann) - primary maintainer of SvelteKit for much of 2021
- [bluwy](https://github.com/bluwy) - major contributor across SvelteKit, vite-plugin-svelte, and Vite
- [dominikg](https://github.com/dominikg) - creator of vite-plugin-svelte
- [dummdidumm](https://github.com/dummdidumm) - maintainer of language-tools, which includes the VS Code extension and `svelte-check`
- [ehrencrona](https://github.com/ehrencrona) - contributor to SvelteKit and uses Svelte at work
- [geoffrich](https://github.com/geoffrich) - has driven efforts to improve the accessibility of the Svelte site and documentation
- [GrygrFlzr](https://github.com/GrygrFlzr) - holds a unique status as a maintainer of both SvelteKit and Vite
- [Halfnelson](https://github.com/Halfnelson) - creator of svelte-native
- [ignatiusmb](https://github.com/ignatiusmb) - regular SvelteKit contributor especially to TypeScript support
- [jasonlyu123](https://github.com/jasonlyu123) - maintainer of language-tools, which includes the VS Code extension and `svelte-check`
- [kaisermann](https://github.com/kaisermann) - creator of svelte-preprocess
- [RedHatter](https://github.com/RedHatter) - creator of Svelte Devtools
- [rixo](https://github.com/rixo) - creator of svelte-hmr
Svelte began accepting donations via [OpenCollective](https://opencollective.com/svelte) last year and has now had over $60,000 donated to-date with [Cohere](https://cohere.ai/) giving $10,000 just today. We hope that these funds will allow existing maintainers to spend more time on Svelte or that the funds could otherwise support Svelte on a part-time or contract basis, which we will continue to investigate.
## Partnerships
Multiple major cloud vendors are stepping up to make deploying SvelteKit applications anywhere a seamless experience. As a result of Rich’s new job, SvelteKit will soon run on [Vercel Edge Functions](https://vercel.com/features/edge-functions). Netlify has made [big contributions](https://github.com/sveltejs/kit/pull/2113) to the SvelteKit Netlify adapter and also [updated](https://github.com/dependents/node-precinct/pull/88) their zip-it-and-ship-it tool to better support SvelteKit. The recent [Cloudflare Pages launch](https://blog.cloudflare.com/cloudflare-pages-goes-full-stack/) featured SvelteKit as a day one partner via a [new adapter](https://github.com/sveltejs/kit/tree/master/packages/adapter-cloudflare) written by Svelte maintainers [pngwn](https://twitter.com/evilpingwin) and [lukeed](https://twitter.com/lukeed05), the latter of whom joined Cloudflare in 2021. [Begin](https://begin.com) created a [SvelteKit adapter](https://github.com/architect/sveltekit-adapter) for [Architect](https://arc.codes) apps. And community members have [contributed adapters](https://sveltesociety.dev/components#adapters) for environments such as Firebase and Deno, showcasing SvelteKit’s ability to run wherever JavaScript does.
We’ve also been working closely with the [Vite](https://vitejs.dev) team to iron out SSR issues uncovered by SvelteKit users. Vite is the build tool that makes the SvelteKit developer experience possible, and thanks to hard work from a contributor base that includes representatives of multiple frameworks, recent releases have solved almost all the issues we’ve been tracking as SvelteKit 1.0 release blockers.
## A growing community
[SvelteSociety](https://sveltesociety.dev/) just hosted the [4th Svelte Summit](https://sveltesummit.com/) — [read a summary here](https://svelte.dev/blog/whats-new-in-svelte-december-2021#what-happened-at-svelte-summit) — and Kevin Åberg Kultalahti is [going full-time to lead SvelteSociety](https://twitter.com/kevmodrome/status/1463151477174714373). In addition to hosting Svelte Summit, Kevin and SvelteSociety host and manage the [Svelte Radio podcast](https://www.svelteradio.com/), the [SvelteSociety YouTube channel](https://www.youtube.com/SvelteSociety), and the [Svelte subreddit](https://www.reddit.com/r/sveltejs). SvelteSociety has become the home of all things related to the Svelte community, with the sveltejs/community and sveltejs/integrations repos being retired in favor of [sveltesociety.dev](https://sveltesociety.dev/), which has been redesigned and rebuilt in SvelteKit. In October [Brittney Postma](https://github.com/brittneypostma), [Willow aka GHOST](https://ghostdev.xyz), [Steph Dietz](https://github.com/StephDietz), and [Gen Ashley](https://twitter.com/coderinheels) founded [Svelte Sirens](https://sveltesirens.dev/), a group for women & non-binary community members and their allies.
Hundreds of developers join the Svelte Discord every week to chat about Svelte. You may have noticed that, as of recently, some members of the server have purple names. These are people with the ambassadors role, which was created to recognise some of the community’s most valued members and help manage the demands of a rapidly growing community. Svelte ambassadors are people who are well known for their helpfulness and contributions and for upholding Svelte’s reputation as a friendly, welcoming community, and we’re deeply grateful for their involvement. The initial ambassadors in alphabetical order are:
We’re also testing out [GitHub discussions on SvelteKit](https://github.com/sveltejs/kit/discussions) and may bring this to other repos in the Svelte organization if feedback is positive.
## Things to watch
SvelteKit is continuing to progress towards 1.0 and, in just the past week, we have added major features like [improved client-only rendering](https://github.com/sveltejs/kit/pull/2804), [routing hooks](https://github.com/sveltejs/kit/pull/3293), and [the ability to pass data from child components to layouts](https://github.com/sveltejs/kit/pull/3252) (e.g. to support easier management of `<meta>` tags). We're currently working on a number of other high priority items such as discussing API designs for features like streaming and file uploads and contributing to the upcoming Vite 2.8 release.
While a lot of effort has been going into SvelteKit recently, we continue to progress the entire ecosystem. [Svelte 3.46.0](https://github.com/sveltejs/svelte/blob/master/CHANGELOG.md#3460) was one of our biggest releases in awhile with two major new features added: [constants in markup](https://github.com/sveltejs/rfcs/blob/master/text/0007-markup-constants.md) and [style directives](https://github.com/sveltejs/rfcs/blob/master/text/0008-style-directives.md).
Svelte and SvelteKit’s trajectories have been accelerated by the numerous investments above and there will be many more updates to come — subscribe to the [blog](/blog) via [RSS](https://svelte.dev/blog/rss.xml) or check monthly to be the first to get them.
@ -28,7 +28,7 @@ A `<script>` block contains JavaScript that runs when a component instance is cr
---
Svelte uses the `export` keyword to mark a variable declaration as a *property* or *prop*, which means it becomes accessible to consumers of the component (see the section on [attributes and props](docs#template-syntax-attributes-and-props) for more information).
Svelte uses the `export` keyword to mark a variable declaration as a *property* or *prop*, which means it becomes accessible to consumers of the component (see the section on [attributes and props](/docs#template-syntax-attributes-and-props) for more information).
```sv
<script>
@ -44,7 +44,7 @@ Svelte uses the `export` keyword to mark a variable declaration as a *property*
You can specify a default initial value for a prop. It will be used if the component's consumer doesn't specify the prop on the component (or if its initial value is `undefined`) when instantiating the component. Note that whenever a prop is removed by the consumer, its value is set to `undefined` rather than the initial value.
In development mode (see the [compiler options](docs#compile-time-svelte-compile)), a warning will be printed if no default initial value is provided and the consumer does not specify a value. To squelch this warning, ensure that a default initial value is specified, even if it is `undefined`.
In development mode (see the [compiler options](/docs#compile-time-svelte-compile)), a warning will be printed if no default initial value is provided and the consumer does not specify a value. To squelch this warning, ensure that a default initial value is specified, even if it is `undefined`.
```sv
<script>
@ -57,7 +57,7 @@ In development mode (see the [compiler options](docs#compile-time-svelte-compile
If you export a `const`, `class` or `function`, it is readonly from outside the component. Function *expressions* are valid props, however.
Readonly props can be accessed as properties on the element, tied to the component using [`bind:this` syntax](docs#template-syntax-element-directives-bind-element).
Readonly props can be accessed as properties on the element, tied to the component using [`bind:this` syntax](/docs#template-syntax-element-directives-bind-element).
```sv
<script>
@ -109,7 +109,7 @@ Update expressions (`count += 1`) and property assignments (`obj.x = y`) have th
---
Because Svelte's reactivity is based on assignments, using array methods like `.push()` and `.splice()` won't automatically trigger updates. A subsequent assignment is required to trigger the update. This and more details can also be found in the [tutorial](tutorial/updating-arrays-and-objects).
Because Svelte's reactivity is based on assignments, using array methods like `.push()` and `.splice()` won't automatically trigger updates. A subsequent assignment is required to trigger the update. This and more details can also be found in the [tutorial](/tutorial/updating-arrays-and-objects).
```sv
<script>
@ -191,7 +191,7 @@ If a statement consists entirely of an assignment to an undeclared variable, Sve
---
A *store* is an object that allows reactive access to a value via a simple *store contract*. The [`svelte/store` module](docs#run-time-svelte-store) contains minimal store implementations which fulfil this contract.
A *store* is an object that allows reactive access to a value via a simple *store contract*. The [`svelte/store` module](/docs#run-time-svelte-store) contains minimal store implementations which fulfil this contract.
Any time you have a reference to a store, you can access its value inside a component by prefixing it with the `$` character. This causes Svelte to declare the prefixed variable, subscribe to the store at component initialization and unsubscribe when appropriate.
@ -222,7 +222,7 @@ Local variables (that do not represent store values) must *not* have a `$` prefi
You can create your own stores without relying on [`svelte/store`](docs#run-time-svelte-store), by implementing the *store contract*:
You can create your own stores without relying on [`svelte/store`](/docs#run-time-svelte-store), by implementing the *store contract*:
1. A store must contain a `.subscribe` method, which must accept as its argument a subscription function. This subscription function must be immediately and synchronously called with the store's current value upon calling `.subscribe`. All of a store's active subscription functions must later be synchronously called whenever the store's value changes.
2. The `.subscribe` method must return an unsubscribe function. Calling an unsubscribe function must stop its subscription, and its corresponding subscription function must not be called again by the store.
@ -241,7 +241,7 @@ You can `export` bindings from this block, and they will become exports of the c
You cannot `export default`, since the default export is the component itself.
> Variables defined in `module` scripts are not reactive — reassigning them will not trigger a rerender even though the variable itself will update. For values shared between multiple components, consider using a [store](docs#run-time-svelte-store).
> Variables defined in `module` scripts are not reactive — reassigning them will not trigger a rerender even though the variable itself will update. For values shared between multiple components, consider using a [store](/docs#run-time-svelte-store).
@ -453,6 +453,29 @@ The `{@debug ...}` tag offers an alternative to `console.log(...)`. It logs the
The `{@debug}` tag without any arguments will insert a `debugger` statement that gets triggered when *any* state changes, as opposed to the specified variables.
### {@const ...}
```sv
{@const assignment}
```
---
The `{@const ...}` tag defines a local constant.
```sv
<script>
export let boxes;
</script>
{#each boxes as box}
{@const area = box.width * box.height}
{box.width} * {box.height} = {area}
{/each}
```
`{@const}` is only allowed as direct child of `{#each}`, `{:then}`, `{:catch}`, `<Component />` or `<svelte:fragment />`.
### Element directives
@ -821,6 +844,46 @@ A `class:` directive provides a shorter way of toggling a class on an element.
When `style:` directives are combined with `style` attributes, the directives will take precedence:
```sv
<divstyle="color: blue;"style:color="red">This will be red</div>
```
#### use:*action*
@ -929,7 +992,7 @@ The `transition:` directive indicates a *bidirectional* transition, which means
{/if}
```
> By default intro transitions will not play on first render. You can modify this behaviour by setting `intro: true` when you [create a component](docs#run-time-client-side-component-api).
> By default intro transitions will not play on first render. You can modify this behaviour by setting `intro: true` when you [create a component](/docs#run-time-client-side-component-api).
##### Transition parameters
@ -1022,7 +1085,7 @@ A custom transition function can also return a `tick` function, which is called
{/if}
```
If a transition returns a function instead of a transition object, the function will be called in the next microtask. This allows multiple transitions to coordinate, making [crossfade effects](tutorial/deferred-transitions) possible.
If a transition returns a function instead of a transition object, the function will be called in the next microtask. This allows multiple transitions to coordinate, making [crossfade effects](/tutorial/deferred-transitions) possible.
##### Transition events
@ -1148,9 +1211,9 @@ DOMRect {
---
An animation is triggered when the contents of a [keyed each block](docs#template-syntax-each) are re-ordered. Animations do not run when an element is added or removed, only when the index of an existing data item within the each block changes. Animate directives must be on an element that is an *immediate* child of a keyed each block.
An animation is triggered when the contents of a [keyed each block](/docs#template-syntax-each) are re-ordered. Animations do not run when an element is added or removed, only when the index of an existing data item within the each block changes. Animate directives must be on an element that is an *immediate* child of a keyed each block.
Animations can be used with Svelte's [built-in animation functions](docs#run-time-svelte-animate) or [custom animation functions](docs#template-syntax-element-directives-animate-fn-custom-animation-functions).
Animations can be used with Svelte's [built-in animation functions](/docs#run-time-svelte-animate) or [custom animation functions](/docs#template-syntax-element-directives-animate-fn-custom-animation-functions).
```sv
<!-- When `list` is reordered the animation will run-->
@ -1257,7 +1320,7 @@ on:eventname={handler}
---
Components can emit events using [createEventDispatcher](docs#run-time-svelte-createeventdispatcher), or by forwarding DOM events. Listening for component events looks the same as listening for DOM events:
Components can emit events using [createEventDispatcher](/docs#run-time-svelte-createeventdispatcher), or by forwarding DOM events. Listening for component events looks the same as listening for DOM events:
```sv
<SomeComponenton:whatever={handler}/>
@ -1608,6 +1671,7 @@ All except `scrollX` and `scrollY` are readonly.
<svelte:windowbind:scrollY={y}/>
```
> Note that the page will not be scrolled to the initial value to avoid accessibility issues. Only subsequent changes to the bound variable of `scrollX` and `scrollY` will cause scrolling. However, if the scrolling behaviour is desired, call `scrollTo()` in `onMount()`.
### `<svelte:body>`
@ -1617,7 +1681,7 @@ All except `scrollX` and `scrollY` are readonly.
---
Similarly to `<svelte:window>`, this element allows you to add listeners to events on `document.body`, such as `mouseenter` and `mouseleave`, which don't fire on `window`. It also lets you use [actions](docs#template-syntax-element-directives-use-action) on the `<body>` element.
Similarly to `<svelte:window>`, this element allows you to add listeners to events on `document.body`, such as `mouseenter` and `mouseleave`, which don't fire on `window`. It also lets you use [actions](/docs#template-syntax-element-directives-use-action) on the `<body>` element.
`<svelte:body>` also has to appear at the top level of your component.
@ -1644,7 +1708,7 @@ As with `<svelte:window>` and `<svelte:body>`, this element has to appear at the
@ -1657,7 +1721,7 @@ As with `<svelte:window>` and `<svelte:body>`, this element has to appear at the
---
The `<svelte:options>` element provides a place to specify per-component compiler options, which are detailed in the [compiler section](docs#compile-time-svelte-compile). The possible options are:
The `<svelte:options>` element provides a place to specify per-component compiler options, which are detailed in the [compiler section](/docs#compile-time-svelte-compile). The possible options are:
* `immutable={true}` — you never use mutable data, so the compiler can do simple referential equality checks to determine if values have changed
* `immutable={false}` — the default. Svelte will be more conservative about whether or not mutable objects have changed
@ -1672,7 +1736,7 @@ The `<svelte:options>` element provides a place to specify per-component compile
### `<svelte:fragment>`
The `<svelte:fragment>` element allows you to place content in a [named slot](docs#template-syntax-slot-slot-name) without wrapping it in a container DOM element. This keeps the flow layout of your document intact.
The `<svelte:fragment>` element allows you to place content in a [named slot](/docs#template-syntax-slot-slot-name) without wrapping it in a container DOM element. This keeps the flow layout of your document intact.
The `onMount` function schedules a callback to run as soon as the component has been mounted to the DOM. It must be called during the component's initialisation (but doesn't need to live *inside* the component; it can be called from an external module).
`onMount` does not run inside a [server-side component](docs#run-time-server-side-component-api).
`onMount` does not run inside a [server-side component](/docs#run-time-server-side-component-api).
Creates an event dispatcher that can be used to dispatch [component events](docs#template-syntax-component-directives-on-component-event). Event dispatchers are functions that can take two arguments: `name` and `detail`.
Creates an event dispatcher that can be used to dispatch [component events](/docs#template-syntax-component-directives-on-component-event). Event dispatchers are functions that can take two arguments: `name` and `detail`.
Component events created with `createEventDispatcher` create a [CustomEvent](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent). These events do not [bubble](https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events#Event_bubbling_and_capture) and are not cancellable with `event.preventDefault()`. The `detail` argument corresponds to the [CustomEvent.detail](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/detail) property and can contain any type of data.
@ -256,11 +256,11 @@ Events dispatched from child components can be listened to in their parent. Any
### `svelte/store`
The `svelte/store` module exports functions for creating [readable](docs#run-time-svelte-store-readable), [writable](docs#run-time-svelte-store-writable) and [derived](docs#run-time-svelte-store-derived) stores.
The `svelte/store` module exports functions for creating [readable](/docs#run-time-svelte-store-readable), [writable](/docs#run-time-svelte-store-writable) and [derived](/docs#run-time-svelte-store-derived) stores.
Keep in mind that you don't *have* to use these functions to enjoy the [reactive `$store` syntax](docs#component-format-script-4-prefix-stores-with-$-to-access-their-values) in your components. Any object that correctly implements `.subscribe`, unsubscribe, and (optionally) `.set` is a valid store, and will work both with the special syntax, and with Svelte's built-in [`derived` stores](docs#run-time-svelte-store-derived).
Keep in mind that you don't *have* to use these functions to enjoy the [reactive `$store` syntax](/docs#component-format-script-4-prefix-stores-with-$-to-access-their-values) in your components. Any object that correctly implements `.subscribe`, unsubscribe, and (optionally) `.set` is a valid store, and will work both with the special syntax, and with Svelte's built-in [`derived` stores](/docs#run-time-svelte-store-derived).
This makes it possible to wrap almost any other reactive state handling library for use in Svelte. Read more about the [store contract](docs#component-format-script-4-prefix-stores-with-$-to-access-their-values-store-contract) to see what a correct implementation looks like.
This makes it possible to wrap almost any other reactive state handling library for use in Svelte. Read more about the [store contract](/docs#component-format-script-4-prefix-stores-with-$-to-access-their-values-store-contract) to see what a correct implementation looks like.
#### `writable`
@ -445,8 +445,8 @@ store = tweened(value: any, options)
Tweened stores update their values over a fixed duration. The following options are available:
* `delay` (`number`, default 0) — milliseconds before starting
* `duration` (`number`, default 400) — milliseconds the tween lasts
`store.set` and `store.update` can accept a second `options` argument that will override the options passed in upon instantiation.
@ -537,11 +537,11 @@ A `spring` store gradually changes to its target value based on its `stiffness`
---
As with [`tweened`](docs#run-time-svelte-motion-tweened) stores, `set` and `update` return a Promise that resolves if the spring settles. The `store.stiffness` and `store.damping` properties can be changed while the spring is in motion, and will take immediate effect.
As with [`tweened`](/docs#run-time-svelte-motion-tweened) stores, `set` and `update` return a Promise that resolves if the spring settles. The `store.stiffness` and `store.damping` properties can be changed while the spring is in motion, and will take immediate effect.
Both `set` and `update` can take a second argument — an object with `hard` or `soft` properties. `{ hard: true }` sets the target value immediately; `{ soft: n }` preserves existing momentum for `n` seconds before settling. `{ soft: true }` is equivalent to `{ soft: 0.5 }`.
[See a full example on the spring tutorial.](tutorial/spring)
[See a full example on the spring tutorial.](/tutorial/spring)
```sv
<script>
@ -565,7 +565,7 @@ $: $size = big ? 100 : 10;
### `svelte/transition`
The `svelte/transition` module exports seven functions: `fade`, `blur`, `fly`, `slide`, `scale`, `draw` and `crossfade`. They are for use with Svelte [`transitions`](docs#template-syntax-element-directives-transition-fn).
The `svelte/transition` module exports seven functions: `fade`, `blur`, `fly`, `slide`, `scale`, `draw` and `crossfade`. They are for use with Svelte [`transitions`](/docs#template-syntax-element-directives-transition-fn).
#### `fade`
@ -587,9 +587,9 @@ Animates the opacity of an element from 0 to the current opacity for `in` transi
* `delay` (`number`, default 0) — milliseconds before starting
* `duration` (`number`, default 400) — milliseconds the transition lasts
* `easing` (`function`, default `linear`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `linear`) — an [easing function](/docs#run-time-svelte-easing)
You can see the `fade` transition in action in the [transition tutorial](tutorial/transition).
You can see the `fade` transition in action in the [transition tutorial](/tutorial/transition).
```sv
<script>
@ -623,7 +623,7 @@ Animates a `blur` filter alongside an element's opacity.
* `delay` (`number`, default 0) — milliseconds before starting
* `duration` (`number`, default 400) — milliseconds the transition lasts
* `easing` (`function`, default `cubicInOut`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `cubicInOut`) — an [easing function](/docs#run-time-svelte-easing)
* `opacity` (`number`, default 0) - the opacity value to animate out to and in from
* `amount` (`number`, default 5) - the size of the blur in pixels
@ -659,12 +659,12 @@ Animates the x and y positions and the opacity of an element. `in` transitions a
* `delay` (`number`, default 0) — milliseconds before starting
* `duration` (`number`, default 400) — milliseconds the transition lasts
* `easing` (`function`, default `cubicOut`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `cubicOut`) — an [easing function](/docs#run-time-svelte-easing)
* `x` (`number`, default 0) - the x offset to animate out to and in from
* `y` (`number`, default 0) - the y offset to animate out to and in from
* `opacity` (`number`, default 0) - the opacity value to animate out to and in from
You can see the `fly` transition in action in the [transition tutorial](tutorial/adding-parameters-to-transitions).
You can see the `fly` transition in action in the [transition tutorial](/tutorial/adding-parameters-to-transitions).
```sv
<script>
@ -699,7 +699,7 @@ Slides an element in and out.
* `delay` (`number`, default 0) — milliseconds before starting
* `duration` (`number`, default 400) — milliseconds the transition lasts
* `easing` (`function`, default `cubicOut`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `cubicOut`) — an [easing function](/docs#run-time-svelte-easing)
```sv
<script>
@ -734,7 +734,7 @@ Animates the opacity and scale of an element. `in` transitions animate from an e
* `delay` (`number`, default 0) — milliseconds before starting
* `duration` (`number`, default 400) — milliseconds the transition lasts
* `easing` (`function`, default `cubicOut`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `cubicOut`) — an [easing function](/docs#run-time-svelte-easing)
* `start` (`number`, default 0) - the scale value to animate out to and in from
* `opacity` (`number`, default 0) - the opacity value to animate out to and in from
@ -772,7 +772,7 @@ Animates the stroke of an SVG element, like a snake in a tube. `in` transitions
* `delay` (`number`, default 0) — milliseconds before starting
* `speed` (`number`, default undefined) - the speed of the animation, see below.
* `easing` (`function`, default `cubicInOut`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `cubicInOut`) — an [easing function](/docs#run-time-svelte-easing)
The `speed` parameter is a means of setting the duration of the transition relative to the path's length. It is a modifier that is applied to the length of the path: `duration = length / speed`. A path that is 1000 pixels with a speed of 1 will have a duration of `1000ms`, setting the speed to `0.5` will double that duration and setting it to `2` will halve it.
@ -799,7 +799,7 @@ The `speed` parameter is a means of setting the duration of the transition relat
#### `crossfade`
The `crossfade` function creates a pair of [transitions](docs#template-syntax-element-directives-transition-fn) called `send` and `receive`. When an element is 'sent', it looks for a corresponding element being 'received', and generates a transition that transforms the element to its counterpart's position and fades it out. When an element is 'received', the reverse happens. If there is no counterpart, the `fallback` transition is used.
The `crossfade` function creates a pair of [transitions](/docs#template-syntax-element-directives-transition-fn) called `send` and `receive`. When an element is 'sent', it looks for a corresponding element being 'received', and generates a transition that transforms the element to its counterpart's position and fades it out. When an element is 'received', the reverse happens. If there is no counterpart, the `fallback` transition is used.
---
@ -807,8 +807,8 @@ The `crossfade` function creates a pair of [transitions](docs#template-syntax-el
* `delay` (`number`, default 0) — milliseconds before starting
* `easing` (`function`, default `cubicOut`) — an [easing function](docs#run-time-svelte-easing)
* `fallback` (`function`) — A fallback [transition](docs#template-syntax-element-directives-transition-fn) to use for send when there is no matching element being received, and for receive when there is no element being sent.
* `easing` (`function`, default `cubicOut`) — an [easing function](/docs#run-time-svelte-easing)
* `fallback` (`function`) — A fallback [transition](/docs#template-syntax-element-directives-transition-fn) to use for send when there is no matching element being received, and for receive when there is no element being sent.
```sv
<script>
@ -831,7 +831,7 @@ The `crossfade` function creates a pair of [transitions](docs#template-syntax-el
### `svelte/animate`
The `svelte/animate` module exports one function for use with Svelte [animations](docs#template-syntax-element-directives-animate-fn).
The `svelte/animate` module exports one function for use with Svelte [animations](/docs#template-syntax-element-directives-animate-fn).
#### `flip`
@ -845,7 +845,7 @@ The `flip` function calculates the start and end position of an element and anim
* `delay` (`number`, default 0) — milliseconds before starting
* `easing` (`function`, default `cubicOut`) — an [easing function](docs#run-time-svelte-easing)
* `easing` (`function`, default `cubicOut`) — an [easing function](/docs#run-time-svelte-easing)
`duration` can be provided as either:
@ -855,7 +855,7 @@ The `flip` function calculates the start and end position of an element and anim
---
You can see a full example on the [animations tutorial](tutorial/animate)
You can see a full example on the [animations tutorial](/tutorial/animate)
```sv
@ -879,7 +879,7 @@ You can see a full example on the [animations tutorial](tutorial/animate)
Easing functions specify the rate of change over time and are useful when working with Svelte's built-in transitions and animations as well as the tweened and spring utilities. `svelte/easing` contains 31 named exports, a `linear` ease and 3 variants of 10 different easing functions: `in`, `out` and `inOut`.
You can explore the various eases using the [ease visualiser](examples#easing) in the [examples section](examples).
You can explore the various eases using the [ease visualiser](/examples/easing) in the [examples section](/examples).
| ease | in | out | inOut |
@ -961,7 +961,7 @@ Existing children of `target` are left where they are.
---
The `hydrate` option instructs Svelte to upgrade existing DOM (usually from server-side rendering) rather than creating new elements. It will only work if the component was compiled with the [`hydratable: true` option](docs#compile-time-svelte-compile). Hydration of `<head>` elements only works properly if the server-side rendering code was also compiled with `hydratable: true`, which adds a marker to each element in the `<head>` so that the component knows which elements it's responsible for removing during hydration.
The `hydrate` option instructs Svelte to upgrade existing DOM (usually from server-side rendering) rather than creating new elements. It will only work if the component was compiled with the [`hydratable: true` option](/docs#compile-time-svelte-compile). Hydration of `<head>` elements only works properly if the server-side rendering code was also compiled with `hydratable: true`, which adds a marker to each element in the `<head>` so that the component knows which elements it's responsible for removing during hydration.
Whereas children of `target` are normally left alone, `hydrate: true` will cause any children to be removed. For that reason, the `anchor` option cannot be used alongside `hydrate: true`.
@ -1045,7 +1045,7 @@ app.count += 1;
---
Svelte components can also be compiled to custom elements (aka web components) using the `customElement: true` compiler option. You should specify a tag name for the component using the `<svelte:options>` [element](docs#template-syntax-svelte-options).
Svelte components can also be compiled to custom elements (aka web components) using the `customElement: true` compiler option. You should specify a tag name for the component using the `<svelte:options>` [element](/docs#template-syntax-svelte-options).
```sv
<svelte:optionstag="my-element"/>
@ -1082,7 +1082,7 @@ document.body.innerHTML = `
---
By default, custom elements are compiled with `accessors: true`, which means that any [props](docs#template-syntax-attributes-and-props) are exposed as properties of the DOM element (as well as being readable/writable as attributes, where possible).
By default, custom elements are compiled with `accessors: true`, which means that any [props](/docs#template-syntax-attributes-and-props) are exposed as properties of the DOM element (as well as being readable/writable as attributes, where possible).
To prevent this, add `accessors={false}` to `<svelte:options>`.
@ -1119,7 +1119,7 @@ Unlike client-side components, server-side components don't have a lifespan afte
A server-side component exposes a `render` method that can be called with optional props. It returns an object with `head`, `html`, and `css` properties, where `head` contains the contents of any `<svelte:head>` elements encountered.
You can import a Svelte component directly into Node using [`svelte/register`](docs#run-time-svelte-register).
You can import a Svelte component directly into Node using [`svelte/register`](/docs#run-time-svelte-register).
The `parse` function parses a component, returning only its abstract syntax tree. Unlike compiling with the `generate: false` option, this will not perform any validation or other analysis of the component beyond parsing it.
The `parse` function parses a component, returning only its abstract syntax tree. Unlike compiling with the `generate: false` option, this will not perform any validation or other analysis of the component beyond parsing it. Note that the returned AST is not considered public API, so breaking changes could occur at any point in time.
@ -213,6 +213,20 @@ Enforce that `on:mouseover` and `on:mouseout` are accompanied by `on:focus` and
---
### `a11y-no-redundant-roles`
Some HTML elements have default ARIA roles. Giving these elements an ARIA role that is already set by the browser [has no effect](https://www.w3.org/TR/using-aria/#aria-does-nothing) and is redundant.
```sv
<!-- A11y: Redundant role 'button' -->
<buttonrole="button"/>
<!-- A11y: Redundant role 'img' -->
<imgrole="img"src="foo.jpg"/>
```
---
### `a11y-positive-tabindex`
Avoid positive `tabindex` property values. This will move elements out of the expected tab order, creating a confusing experience for keyboard users.
question: I'm new to Svelte. Where should I start?
---
We think the best way to get started is playing through the interactive [Tutorial](tutorial). Each step there is mainly focused on one specific aspect and is easy to follow. You'll be editing and running real Svelte components right in your browser.
We think the best way to get started is playing through the interactive [Tutorial](/tutorial). Each step there is mainly focused on one specific aspect and is easy to follow. You'll be editing and running real Svelte components right in your browser.
Five to ten minutes should be enough to get you up and running. An hour and a half should get you through the entire tutorial.
Five to ten minutes should be enough to get you up and running. An hour and a half should get you through the entire tutorial.
Welcome to the Svelte tutorial. This will teach you everything you need to know to build fast, small web applications easily.
You can also consult the [API docs](docs) and the [examples](examples), or — if you're impatient to start hacking on your machine locally — the [60-second quickstart](blog/the-easiest-way-to-get-started).
You can also consult the [API docs](/docs) and the [examples](/examples), or — if you're impatient to start hacking on your machine locally — the [60-second quickstart](/blog/the-easiest-way-to-get-started).
@ -12,9 +12,9 @@ First, you'll need to integrate Svelte with a build tool. There are officially m
...and a variety of [community-maintained ones](https://sveltesociety.dev/tools).
Don't worry if you're relatively new to web development and haven't used these tools before. We've prepared a simple step-by-step guide, [Svelte for new developers](blog/svelte-for-new-developers), which walks you through the process.
Don't worry if you're relatively new to web development and haven't used these tools before. We've prepared a simple step-by-step guide, [Svelte for new developers](/blog/svelte-for-new-developers), which walks you through the process.
You'll also want to configure your text editor. There are [plugins](https://sveltesociety.dev/tools#editor-support) for many popular editors as well as an official [VS Code extension](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode). If your editor does not have a Svelte plugin then you can follow [this guide](blog/setting-up-your-editor) to configure your text editor to treat `.svelte` files the same as `.html` for the sake of syntax highlighting.
You'll also want to configure your text editor. There are [plugins](https://sveltesociety.dev/tools#editor-support) for many popular editors as well as an official [VS Code extension](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode). If your editor does not have a Svelte plugin then you can follow [this guide](/blog/setting-up-your-editor) to configure your text editor to treat `.svelte` files the same as `.html` for the sake of syntax highlighting.
Then, once you've got your project set up, using Svelte components is easy. The compiler turns each component into a regular JavaScript class — just import it and instantiate with `new`:
@ -30,4 +30,4 @@ const app = new App({
});
```
You can then interact with `app` using the [component API](docs#run-time-client-side-component-api) if you need to.
You can then interact with `app` using the [component API](/docs#run-time-client-side-component-api) if you need to.
Unlike DOM events, component events don't *bubble*. If you want to listen to an event on some deeply nested component, the intermediate components must *forward* the event.
In this case, we have the same `App.svelte` and `Inner.svelte` as in the [previous chapter](tutorial/component-events), but there's now an `Outer.svelte` component that contains `<Inner/>`.
In this case, we have the same `App.svelte` and `Inner.svelte` as in the [previous chapter](/tutorial/component-events), but there's now an `Outer.svelte` component that contains `<Inner/>`.
One way we could solve the problem is adding `createEventDispatcher` to `Outer.svelte`, listening for the `message` event, and creating a handler for it:
@ -12,4 +12,4 @@ The readonly `this` binding applies to every element (and component) and allows
></canvas>
```
Note that the value of `canvas` will be `undefined` until the component has mounted, so we put the logic inside the `onMount` [lifecycle function](tutorial/onmount).
Note that the value of `canvas` will be `undefined` until the component has mounted, so we put the logic inside the `onMount` [lifecycle function](/tutorial/onmount).
Every component has a *lifecycle* that starts when it is created, and ends when it is destroyed. There are a handful of functions that allow you to run code at key moments during that lifecycle.
The one you'll use most frequently is `onMount`, which runs after the component is first rendered to the DOM. We briefly encountered it [earlier](tutorial/bind-this) when we needed to interact with a `<canvas>` element after it had been rendered.
The one you'll use most frequently is `onMount`, which runs after the component is first rendered to the DOM. We briefly encountered it [earlier](/tutorial/bind-this) when we needed to interact with a `<canvas>` element after it had been rendered.
We'll add an `onMount` handler that loads some data over the network:
Not all application state belongs inside your application's component hierarchy. Sometimes, you'll have values that need to be accessed by multiple unrelated components, or by a regular JavaScript module.
In Svelte, we do this with *stores*. A store is simply an object with a `subscribe` method that allows interested parties to be notified whenever the store value changes. In `App.svelte`, `count` is a store, and we're setting `count_value` in the `count.subscribe` callback.
In Svelte, we do this with *stores*. A store is simply an object with a `subscribe` method that allows interested parties to be notified whenever the store value changes. In `App.svelte`, `count` is a store, and we're setting `countValue` in the `count.subscribe` callback.
Click the `stores.js` tab to see the definition of `count`. It's a *writable* store, which means it has `set` and `update` methods in addition to `subscribe`.
@ -8,12 +8,12 @@ Start by declaring `unsubscribe` in `App.svelte`:
```js
const unsubscribe = count.subscribe(value => {
count_value = value;
countValue = value;
});
```
> Calling a `subscribe` method returns an `unsubscribe` function.
You now declared `unsubscribe`, but it still needs to be called, for example through the `onDestroy` [lifecycle hook](tutorial/ondestroy):
You now declared `unsubscribe`, but it still needs to be called, for example through the `onDestroy` [lifecycle hook](/tutorial/ondestroy):
```html
<script>
@ -23,16 +23,16 @@ You now declared `unsubscribe`, but it still needs to be called, for example thr
import Decrementer from './Decrementer.svelte';
import Resetter from './Resetter.svelte';
let count_value;
let countValue;
const unsubscribe = count.subscribe(value => {
count_value = value;
countValue = value;
});
onDestroy(unsubscribe);
</script>
<h1>The count is {count_value}</h1>
<h1>The count is {countValue}</h1>
```
It starts to get a bit boilerplatey though, especially if your component subscribes to multiple stores. Instead, Svelte has a trick up its sleeve — you can reference a store value by prefixing the store name with `$`:
> It's possible to derive a store from multiple inputs, and to explicitly `set` a value instead of returning it (which is useful for deriving values asynchronously). Consult the [API reference](docs#run-time-svelte-store-derived) for more information.
> It's possible to derive a store from multiple inputs, and to explicitly `set` a value instead of returning it (which is useful for deriving values asynchronously). Consult the [API reference](/docs#run-time-svelte-store-derived) for more information.
In the [previous chapter](tutorial/deferred-transitions), we used deferred transitions to create the illusion of motion as elements move from one todo list to the other.
In the [previous chapter](/tutorial/deferred-transitions), we used deferred transitions to create the illusion of motion as elements move from one todo list to the other.
To complete the illusion, we also need to apply motion to the elements that *aren't* transitioning. For this, we use the `animate` directive.
@ -11,7 +11,7 @@ There are two halves to the context API — `setContext` and `getContext`. If a
Let's set the context first. In `Map.svelte`, import `setContext` from `svelte` and `key` from `mapbox.js` and call `setContext`:
```js
import { onMount, setContext } from 'svelte';
import { onDestroy, setContext } from 'svelte';
import { mapbox, key } from './mapbox.js';
setContext(key, {
@ -19,7 +19,7 @@ setContext(key, {
});
```
The context object can be anything you like. Like [lifecycle functions](tutorial/onmount), `setContext` and `getContext` must be called during component initialisation. Calling it afterwards - for example inside `onMount` - will throw an error. In this example, since `map` isn't created until the component has mounted, our context object contains a `getMap` function rather than `map` itself.
The context object can be anything you like. Like [lifecycle functions](/tutorial/onmount), `setContext` and `getContext` must be called during component initialisation. Calling it afterwards - for example inside `onMount` - will throw an error. In this example, since `map` isn't created until the component has mounted, our context object contains a `getMap` function rather than `map` itself.
On the other side of the equation, in `MapMarker.svelte`, we can now get a reference to the Mapbox instance:
@ -40,10 +40,10 @@ The markers can now add themselves to the map.
In `mapbox.js` you'll see this line:
```js
const key = {};
const key = Symbol();
```
We can use anything as a key — we could do `setContext('mapbox', ...)` for example. The downside of using a string is that different component libraries might accidentally use the same one; using an object literal means the keys are guaranteed not to conflict in any circumstance (since an object only has referential equality to itself, i.e. `{} !== {}` whereas `"x" === "x"`), even when you have multiple different contexts operating across many component layers.
Technically, we can use any value as a key — we could do `setContext('mapbox', ...)` for example. The downside of using a string is that different component libraries might accidentally use the same one; using [symbols](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol), on the other hand, means that the keys are guaranteed not to conflict in any circumstance, even when you have multiple different contexts operating across many component layers, since a symbol is essentially a unique identifier.
You've now finished the Svelte tutorial and are ready to start building apps. You can refer back to individual chapters at any time (click the title above to reveal a dropdown) or continue your learning via the [API reference](docs), [Examples](examples) and [Blog](blog). If you're a Twitter user, you can get updates via [@sveltejs](https://twitter.com/sveltejs).
You've now finished the Svelte tutorial and are ready to start building apps. You can refer back to individual chapters at any time (click the title above to reveal a dropdown) or continue your learning via the [API reference](/docs), [Examples](/examples) and [Blog](/blog). If you're a Twitter user, you can get updates via [@sveltejs](https://twitter.com/sveltejs).
To get set up in your local development environment, check out [the quickstart guide](blog/the-easiest-way-to-get-started).
To get set up in your local development environment, check out [the quickstart guide](/blog/the-easiest-way-to-get-started).
If you're looking for a more expansive framework that includes routing, server-side rendering and everything else, take a look at [SvelteKit](https://kit.svelte.dev).
Most importantly: since you're now a member of the Svelte community, you should [join our friendly Discord chatroom](chat). That's where you'll find fellow Svelte users, and it's where we plan the future of the framework.
Most importantly: since you're now a member of the Svelte community, you should [join our friendly Discord chatroom](https://svelte.dev/chat). That's where you'll find fellow Svelte users, and it's where we plan the future of the framework.
andirady
5 years ago
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