# Introduction

`eslint-plugin-svelte` is the official [ESLint] plugin for [Svelte].  
It provides many unique check rules by using the template AST.  
You can check on the [Online DEMO](https://sveltejs.github.io/eslint-plugin-svelte/playground/).

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## :name_badge: What is this plugin?

[ESLint] plugin for [Svelte].  
It provides many unique check rules using the AST generated by [svelte-eslint-parser].

### ❗ Attention

The [svelte-eslint-parser] and the `eslint-plugin-svelte` can not be used with the [eslint-plugin-svelte3].

[svelte-eslint-parser]: https://github.com/sveltejs/svelte-eslint-parser
[eslint-plugin-svelte3]: https://github.com/sveltejs/eslint-plugin-svelte3

<!--DOCS_IGNORE_START-->

## Migration Guide

To migrate from `eslint-plugin-svelte` v1, or [`@ota-meshi/eslint-plugin-svelte`](https://www.npmjs.com/package/@ota-meshi/eslint-plugin-svelte), please refer to the [migration guide](https://sveltejs.github.io/eslint-plugin-svelte/migration/).

## :book: Documentation

See [documents](https://sveltejs.github.io/eslint-plugin-svelte/).

## :cd: Installation

```bash
npm install --save-dev eslint eslint-plugin-svelte svelte
```

> **Requirements**
>
> - ESLint v7.0.0 and above
> - Node.js v14.17.x, v16.x and above

<!--DOCS_IGNORE_END-->

## :book: Usage

<!--USAGE_SECTION_START-->
<!--USAGE_GUIDE_START-->

### Configuration

Use `.eslintrc.*` file to configure rules. See also: <https://eslint.org/docs/user-guide/configuring>.

Example **.eslintrc.js**:

```js
module.exports = {
  extends: [
    // add more generic rule sets here, such as:
    // 'eslint:recommended',
    'plugin:svelte/recommended'
  ],
  rules: {
    // override/add rules settings here, such as:
    // 'svelte/rule-name': 'error'
  }
};
```

This plugin provides configs:

- `plugin:svelte/base` ... Configuration to enable correct Svelte parsing.
- `plugin:svelte/recommended` ... Above, plus rules to prevent errors or unintended behavior.
- `plugin:svelte/prettier` ... Turns off rules that may conflict with [Prettier](https://prettier.io/) (You still need to configure prettier to work with svelte yourself, for example by using [prettier-plugin-svelte](https://github.com/sveltejs/prettier-plugin-svelte).).
- `plugin:svelte/all` ... All rules. This configuration is not recommended for production use because it changes with every minor and major version of `eslint-plugin-svelte`. Use it at your own risk.

See [the rule list](https://sveltejs.github.io/eslint-plugin-svelte/rules/) to get the `rules` that this plugin provides.

::: warning ❗ Attention

The `eslint-plugin-svelte` can not be used with the [eslint-plugin-svelte3].
If you are using [eslint-plugin-svelte3] you need to remove it.

```diff
  "plugins": [
-   "svelte3"
  ]
```

:::

#### Parser Configuration

If you have specified a parser, you need to configure a parser for `.svelte`.

For example, if you are using the `"@babel/eslint-parser"`, configure it as follows:

```js
module.exports = {
  // ...
  extends: ['plugin:svelte/recommended'],
  // ...
  parser: '@babel/eslint-parser',
  // Add an `overrides` section to add a parser configuration for svelte.
  overrides: [
    {
      files: ['*.svelte'],
      parser: 'svelte-eslint-parser'
    }
    // ...
  ]
  // ...
};
```

For example, if you are using the `"@typescript-eslint/parser"`, and if you want to use TypeScript in `<script>` of `.svelte`, you need to add more `parserOptions` configuration.

```js
module.exports = {
  // ...
  extends: ['plugin:svelte/recommended'],
  // ...
  parser: '@typescript-eslint/parser',
  parserOptions: {
    // ...
    project: 'path/to/your/tsconfig.json',
    extraFileExtensions: ['.svelte'] // This is a required setting in `@typescript-eslint/parser` v4.24.0.
  },
  overrides: [
    {
      files: ['*.svelte'],
      parser: 'svelte-eslint-parser',
      // Parse the `<script>` in `.svelte` as TypeScript by adding the following configuration.
      parserOptions: {
        parser: '@typescript-eslint/parser'
      }
    }
    // ...
  ]
  // ...
};
```

If you have a mix of TypeScript and JavaScript in your project, use a multiple parser configuration.

```js
module.exports = {
  // ...
  overrides: [
    {
      files: ['*.svelte'],
      parser: 'svelte-eslint-parser',
      parserOptions: {
        parser: {
          // Specify a parser for each lang.
          ts: '@typescript-eslint/parser',
          js: 'espree',
          typescript: '@typescript-eslint/parser'
        }
      }
    }
    // ...
  ]
  // ...
};
```

See also <https://github.com/sveltejs/svelte-eslint-parser#readme>.

::: warning ❗ Attention

The TypeScript parser uses a singleton internally and it will only use the
options given to it when it was first initialized. If trying to change the
options for a different file or override, the parser will simply ignore the new
options (which may result in an error). See
[typescript-eslint/typescript-eslint#6778](https://github.com/typescript-eslint/typescript-eslint/issues/6778)
for some context.

:::

#### settings.svelte

You can change the behavior of this plugin with some settings.

e.g.

```js
module.exports = {
  // ...
  settings: {
    svelte: {
      ignoreWarnings: [
        '@typescript-eslint/no-unsafe-assignment',
        '@typescript-eslint/no-unsafe-member-access'
      ],
      compileOptions: {
        postcss: {
          configFilePath: './path/to/my/postcss.config.js'
        }
      },
      kit: {
        files: {
          routes: 'src/routes'
        }
      }
    }
  }
  // ...
};
```

#### settings.svelte.ignoreWarnings

Specifies an array of rules that ignore reports in the template.  
For example, set rules on the template that cannot avoid false positives.

#### settings.svelte.compileOptions

Specifies options for Svelte compile. Effects rules that use Svelte compile. The target rules are [svelte/valid-compile](https://sveltejs.github.io/eslint-plugin-svelte/rules/valid-compile/) and [svelte/no-unused-svelte-ignore](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-unused-svelte-ignore/). **Note that it has no effect on ESLint's custom parser**.

- `postcss` ... Specifies options related to PostCSS. You can disable the PostCSS process by specifying `false`.
  - `configFilePath` ... Specifies the path of the directory containing the PostCSS configuration.

#### settings.svelte.kit

If you use SvelteKit with not default configuration, you need to set below configurations.
The schema is subset of SvelteKit's configuration.
Therefore please check [SvelteKit docs](https://kit.svelte.dev/docs/configuration) for more details.

e.g.

```js
module.exports = {
  // ...
  settings: {
    svelte: {
      kit: {
        files: {
          routes: 'src/routes'
        }
      }
    }
  }
  // ...
};
```

### Running ESLint from the command line

If you want to run `eslint` from the command line, make sure you include the `.svelte` extension using [the `--ext` option](https://eslint.org/docs/user-guide/configuring#specifying-file-extensions-to-lint) or a glob pattern, because ESLint targets only `.js` files by default.

Examples:

```bash
eslint --ext .js,.svelte src
eslint "src/**/*.{js,svelte}"
```

## :computer: Editor Integrations

### Visual Studio Code

Use the [dbaeumer.vscode-eslint](https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint) extension that Microsoft provides officially.

You have to configure the `eslint.validate` option of the extension to check `.svelte` files, because the extension targets only `*.js` or `*.jsx` files by default.

Example **.vscode/settings.json**:

```json
{
  "eslint.validate": ["javascript", "javascriptreact", "svelte"]
}
```

<!--USAGE_GUIDE_END-->
<!--USAGE_SECTION_END-->

## :white_check_mark: Rules

<!-- prettier-ignore-start -->
<!--RULES_SECTION_START-->

:wrench: Indicates that the rule is fixable, and using `--fix` option on the [command line](https://eslint.org/docs/user-guide/command-line-interface#fixing-problems) can automatically fix some of the reported problems.  
:bulb: Indicates that some problems reported by the rule are manually fixable by editor [suggestions](https://eslint.org/docs/developer-guide/working-with-rules#providing-suggestions).  
:star: Indicates that the rule is included in the `plugin:svelte/recommended` config.

<!--RULES_TABLE_START-->

## Possible Errors

These rules relate to possible syntax or logic errors in Svelte code:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/infinite-reactive-loop](https://sveltejs.github.io/eslint-plugin-svelte/rules/infinite-reactive-loop/) | Svelte runtime prevents calling the same reactive statement twice in a microtask. But between different microtask, it doesn't prevent. |  |
| [svelte/no-dom-manipulating](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-dom-manipulating/) | disallow DOM manipulating |  |
| [svelte/no-dupe-else-if-blocks](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-dupe-else-if-blocks/) | disallow duplicate conditions in `{#if}` / `{:else if}` chains | :star: |
| [svelte/no-dupe-on-directives](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-dupe-on-directives/) | disallow duplicate `on:` directives |  |
| [svelte/no-dupe-style-properties](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-dupe-style-properties/) | disallow duplicate style properties | :star: |
| [svelte/no-dupe-use-directives](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-dupe-use-directives/) | disallow duplicate `use:` directives |  |
| [svelte/no-dynamic-slot-name](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-dynamic-slot-name/) | disallow dynamic slot name | :star::wrench: |
| [svelte/no-export-load-in-svelte-module-in-kit-pages](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-export-load-in-svelte-module-in-kit-pages/) | disallow exporting load functions in `*.svelte` module in SvelteKit page components. |  |
| [svelte/no-not-function-handler](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-not-function-handler/) | disallow use of not function in event handler | :star: |
| [svelte/no-object-in-text-mustaches](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-object-in-text-mustaches/) | disallow objects in text mustache interpolation | :star: |
| [svelte/no-reactive-reassign](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-reactive-reassign/) | disallow reassigning reactive values |  |
| [svelte/no-shorthand-style-property-overrides](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-shorthand-style-property-overrides/) | disallow shorthand style properties that override related longhand properties | :star: |
| [svelte/no-store-async](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-store-async/) | disallow using async/await inside svelte stores because it causes issues with the auto-unsubscribing features |  |
| [svelte/no-unknown-style-directive-property](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-unknown-style-directive-property/) | disallow unknown `style:property` | :star: |
| [svelte/require-store-callbacks-use-set-param](https://sveltejs.github.io/eslint-plugin-svelte/rules/require-store-callbacks-use-set-param/) | store callbacks must use `set` param |  |
| [svelte/require-store-reactive-access](https://sveltejs.github.io/eslint-plugin-svelte/rules/require-store-reactive-access/) | disallow to use of the store itself as an operand. Need to use $ prefix or get function. | :wrench: |
| [svelte/valid-compile](https://sveltejs.github.io/eslint-plugin-svelte/rules/valid-compile/) | disallow warnings when compiling. | :star: |
| [svelte/valid-prop-names-in-kit-pages](https://sveltejs.github.io/eslint-plugin-svelte/rules/valid-prop-names-in-kit-pages/) | disallow props other than data or errors in SvelteKit page components. |  |

## Security Vulnerability

These rules relate to security vulnerabilities in Svelte code:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/no-at-html-tags](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-at-html-tags/) | disallow use of `{@html}` to prevent XSS attack | :star: |
| [svelte/no-target-blank](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-target-blank/) | disallow `target="_blank"` attribute without `rel="noopener noreferrer"` |  |

## Best Practices

These rules relate to better ways of doing things to help you avoid problems:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/block-lang](https://sveltejs.github.io/eslint-plugin-svelte/rules/block-lang/) | disallows the use of languages other than those specified in the configuration for the lang attribute of `<script>` and `<style>` blocks. |  |
| [svelte/button-has-type](https://sveltejs.github.io/eslint-plugin-svelte/rules/button-has-type/) | disallow usage of button without an explicit type attribute |  |
| [svelte/no-at-debug-tags](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-at-debug-tags/) | disallow the use of `{@debug}` | :star: |
| [svelte/no-ignored-unsubscribe](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-ignored-unsubscribe/) | disallow ignoring the unsubscribe method returned by the `subscribe()` on Svelte stores. |  |
| [svelte/no-immutable-reactive-statements](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-immutable-reactive-statements/) | disallow reactive statements that don't reference reactive values. |  |
| [svelte/no-inline-styles](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-inline-styles/) | disallow attributes and directives that produce inline styles |  |
| [svelte/no-reactive-functions](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-reactive-functions/) | it's not necessary to define functions in reactive statements | :bulb: |
| [svelte/no-reactive-literals](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-reactive-literals/) | don't assign literal values in reactive statements | :bulb: |
| [svelte/no-unused-class-name](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-unused-class-name/) | disallow the use of a class in the template without a corresponding style |  |
| [svelte/no-unused-svelte-ignore](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-unused-svelte-ignore/) | disallow unused svelte-ignore comments | :star: |
| [svelte/no-useless-mustaches](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-useless-mustaches/) | disallow unnecessary mustache interpolations | :wrench: |
| [svelte/prefer-destructured-store-props](https://sveltejs.github.io/eslint-plugin-svelte/rules/prefer-destructured-store-props/) | destructure values from object stores for better change tracking & fewer redraws | :bulb: |
| [svelte/require-each-key](https://sveltejs.github.io/eslint-plugin-svelte/rules/require-each-key/) | require keyed `{#each}` block |  |
| [svelte/require-event-dispatcher-types](https://sveltejs.github.io/eslint-plugin-svelte/rules/require-event-dispatcher-types/) | require type parameters for `createEventDispatcher` |  |
| [svelte/require-optimized-style-attribute](https://sveltejs.github.io/eslint-plugin-svelte/rules/require-optimized-style-attribute/) | require style attributes that can be optimized |  |
| [svelte/require-stores-init](https://sveltejs.github.io/eslint-plugin-svelte/rules/require-stores-init/) | require initial value in store |  |
| [svelte/valid-each-key](https://sveltejs.github.io/eslint-plugin-svelte/rules/valid-each-key/) | enforce keys to use variables defined in the `{#each}` block |  |

## Stylistic Issues

These rules relate to style guidelines, and are therefore quite subjective:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/derived-has-same-inputs-outputs](https://sveltejs.github.io/eslint-plugin-svelte/rules/derived-has-same-inputs-outputs/) | derived store should use same variable names between values and callback |  |
| [svelte/first-attribute-linebreak](https://sveltejs.github.io/eslint-plugin-svelte/rules/first-attribute-linebreak/) | enforce the location of first attribute | :wrench: |
| [svelte/html-closing-bracket-spacing](https://sveltejs.github.io/eslint-plugin-svelte/rules/html-closing-bracket-spacing/) | require or disallow a space before tag's closing brackets | :wrench: |
| [svelte/html-quotes](https://sveltejs.github.io/eslint-plugin-svelte/rules/html-quotes/) | enforce quotes style of HTML attributes | :wrench: |
| [svelte/html-self-closing](https://sveltejs.github.io/eslint-plugin-svelte/rules/html-self-closing/) | enforce self-closing style | :wrench: |
| [svelte/indent](https://sveltejs.github.io/eslint-plugin-svelte/rules/indent/) | enforce consistent indentation | :wrench: |
| [svelte/max-attributes-per-line](https://sveltejs.github.io/eslint-plugin-svelte/rules/max-attributes-per-line/) | enforce the maximum number of attributes per line | :wrench: |
| [svelte/mustache-spacing](https://sveltejs.github.io/eslint-plugin-svelte/rules/mustache-spacing/) | enforce unified spacing in mustache | :wrench: |
| [svelte/no-extra-reactive-curlies](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-extra-reactive-curlies/) | disallow wrapping single reactive statements in curly braces | :bulb: |
| [svelte/no-restricted-html-elements](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-restricted-html-elements/) | disallow specific HTML elements |  |
| [svelte/no-spaces-around-equal-signs-in-attribute](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-spaces-around-equal-signs-in-attribute/) | disallow spaces around equal signs in attribute | :wrench: |
| [svelte/prefer-class-directive](https://sveltejs.github.io/eslint-plugin-svelte/rules/prefer-class-directive/) | require class directives instead of ternary expressions | :wrench: |
| [svelte/prefer-style-directive](https://sveltejs.github.io/eslint-plugin-svelte/rules/prefer-style-directive/) | require style directives instead of style attribute | :wrench: |
| [svelte/shorthand-attribute](https://sveltejs.github.io/eslint-plugin-svelte/rules/shorthand-attribute/) | enforce use of shorthand syntax in attribute | :wrench: |
| [svelte/shorthand-directive](https://sveltejs.github.io/eslint-plugin-svelte/rules/shorthand-directive/) | enforce use of shorthand syntax in directives | :wrench: |
| [svelte/sort-attributes](https://sveltejs.github.io/eslint-plugin-svelte/rules/sort-attributes/) | enforce order of attributes | :wrench: |
| [svelte/spaced-html-comment](https://sveltejs.github.io/eslint-plugin-svelte/rules/spaced-html-comment/) | enforce consistent spacing after the `<!--` and before the `-->` in a HTML comment | :wrench: |

## Extension Rules

These rules extend the rules provided by ESLint itself, or other plugins to work well in Svelte:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/no-inner-declarations](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-inner-declarations/) | disallow variable or `function` declarations in nested blocks | :star: |
| [svelte/no-trailing-spaces](https://sveltejs.github.io/eslint-plugin-svelte/rules/no-trailing-spaces/) | disallow trailing whitespace at the end of lines | :wrench: |

## Experimental

:warning: These rules are considered experimental and may change or be removed in the future:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/experimental-require-slot-types](https://sveltejs.github.io/eslint-plugin-svelte/rules/experimental-require-slot-types/) | require slot type declaration using the `$$Slots` interface |  |
| [svelte/experimental-require-strict-events](https://sveltejs.github.io/eslint-plugin-svelte/rules/experimental-require-strict-events/) | require the strictEvents attribute on `<script>` tags |  |

## System

These rules relate to this plugin works:

| Rule ID | Description |    |
|:--------|:------------|:---|
| [svelte/comment-directive](https://sveltejs.github.io/eslint-plugin-svelte/rules/comment-directive/) | support comment-directives in HTML template | :star: |
| [svelte/system](https://sveltejs.github.io/eslint-plugin-svelte/rules/system/) | system rule for working this plugin | :star: |

## Deprecated

- :warning: We're going to remove deprecated rules in the next major release. Please migrate to successor/new rules.
- :innocent: We don't fix bugs which are in deprecated rules since we don't have enough resources.

| Rule ID | Replaced by |
|:--------|:------------|
| [svelte/@typescript-eslint/no-unnecessary-condition](https://sveltejs.github.io/eslint-plugin-svelte/rules/@typescript-eslint/no-unnecessary-condition/) | This rule is no longer needed when using svelte-eslint-parser>=v0.19.0. |

<!--RULES_TABLE_END-->
<!--RULES_SECTION_END-->
<!-- prettier-ignore-end -->

<!--DOCS_IGNORE_START-->

## :beers: Contributing

Welcome contributing!

Please use GitHub's Issues/PRs.

See also [CONTRIBUTING.md](./CONTRIBUTING.md)

### Working With Rules

This plugin uses [svelte-eslint-parser](https://github.com/sveltejs/svelte-eslint-parser) for the parser. Check [here](https://sveltejs.github.io/svelte-eslint-parser/) to find out about AST.

<!--DOCS_IGNORE_END-->

## :lock: License

See the [LICENSE](LICENSE) file for license rights and limitations (MIT).

[svelte]: https://svelte.dev/
[eslint]: https://eslint.org/