astro/packages/integrations/svelte/README.md
Tony Sullivan ce9a61e9fc
Support custom svelte compiler options in @astrojs/svelte (#3181)
* updating svelte integration to allow custom user config

* test: adding a test to verify that svelte options are piped through the integration

* updating the README with docs on overridding svelte options

* chore: adding changeset

* fix: copy/paste bug in test validation

* removing temporary debug scripts
2022-04-22 17:59:20 +00:00

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# @astrojs/svelte 🧡
This **[Astro integration][astro-integration]** enables server-side rendering and client-side hydration for your [Svelte](https://svelte.dev/) components.
## Installation
There are two ways to add integrations to your project. Let's try the most convenient option first!
### (experimental) `astro add` command
Astro includes a CLI tool for adding first party integrations: `astro add`. This command will:
1. (Optionally) Install all necessary dependencies and peer dependencies
2. (Also optionally) Update your `astro.config.*` file to apply this integration
To install `@astrojs/svelte`, run the following from your project directory and follow the prompts:
```sh
# Using NPM
npx astro add svelte
# Using Yarn
yarn astro add svelte
# Using PNPM
pnpx astro add svelte
```
If you run into any hiccups, [feel free to log an issue on our GitHub](https://github.com/withastro/astro/issues) and try the manual installation steps below.
### Install dependencies manually
First, install the `@astrojs/svelte` integration like so:
```
npm install @astrojs/svelte
```
Most package managers will install associated peer dependencies as well. Still, if you see a "Cannot find package 'svelte'" (or similar) warning when you start up Astro, you'll need to install Svelte:
```sh
npm install svelte
```
Now, apply this integration to your `astro.config.*` file using the `integrations` property:
__astro.config.mjs__
```js
import svelte from '@astrojs/svelte';
export default {
// ...
integrations: [svelte()],
}
```
## Getting started
To use your first Svelte component in Astro, head to our [UI framework documentation][astro-ui-frameworks]. You'll explore:
- 📦 how framework components are loaded,
- 💧 client-side hydration options, and
- 🪆 opportunities to mix and nest frameworks together
Also check our [Astro Integration Documentation][astro-integration] for more on integrations.
[astro-integration]: https://docs.astro.build/en/guides/integrations-guide/
[astro-ui-frameworks]: https://docs.astro.build/en/core-concepts/framework-components/#using-framework-components
## Options
This integration is powered by `@sveltejs/vite-plugin-svelte`. To customize the Svelte compiler, options can be provided to the integration. See the `@sveltejs/vite-plugin-svelte` [docs](https://github.com/sveltejs/vite-plugin-svelte/blob/HEAD/docs/config.md) for more details.
### Default options
A few of the default options passed to the Svelte compiler are required to build properly for Astro and cannot be overridden.
```js
const defaultOptions = {
emitCss: true,
compilerOptions: { dev: isDev, hydratable: true },
preprocess: [
preprocess({
less: true,
sass: { renderSync: true },
scss: { renderSync: true },
stylus: true,
typescript: true,
}),
],
};
```
The `emitCss`, `compilerOptions.dev`, and `compilerOptions.hydratable` cannot be overridden.
Providing your own `preprocess` options **will** override the defaults - make sure to enable the preprocessor flags needed for your project.