eslint-plugin-svelte

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.

We are working on experimental support for Svelte v5, but may break with new versions of Svelte v5.

: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

Cannot be used with eslint-plugin-svelte3

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

Experimental support for Svelte v5

We are working on support for Svelte v5, but it is still an experimental feature. Please note that rules and features related to Svelte v5 may be changed or removed in minor versions without notice.

Migration Guide

To migrate from eslint-plugin-svelte v1, or @ota-meshi/eslint-plugin-svelte, please refer to the migration guide.

:book: Documentation

See documents.

:cd: Installation

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

:book: Usage

Configuration

New Config (eslint.config.js)

Use eslint.config.js file to configure rules. See also: https://eslint.org/docs/latest/use/configure/configuration-files-new.

Example eslint.config.js:

import eslintPluginSvelte from 'eslint-plugin-svelte';
export default [
  // add more generic rule sets here, such as:
  // js.configs.recommended,
  ...eslintPluginSvelte.configs['flat/recommended'],
  {
    rules: {
      // override/add rules settings here, such as:
      // 'svelte/rule-name': 'error'
    }
  }
];

This plugin provides configs:

• eslintPluginSvelte.configs['flat/base'] ... Configuration to enable correct Svelte parsing.
• eslintPluginSvelte.configs['flat/recommended'] ... Above, plus rules to prevent errors or unintended behavior.
• eslintPluginSvelte.configs['flat/prettier'] ... Turns off rules that may conflict with Prettier (You still need to configure prettier to work with svelte yourself, for example by using prettier-plugin-svelte.).
• eslintPluginSvelte.configs['flat/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 to get the rules that this plugin provides.

Legacy Config (.eslintrc)

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

Example .eslintrc.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 (You still need to configure prettier to work with svelte yourself, for example by using 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 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.

  "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:

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.

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.

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 for some context.

:::

settings.svelte

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

e.g.

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 and svelte/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 for more details.

e.g.

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 or a glob pattern, because ESLint targets only .js files by default.

Examples:

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

:computer: Editor Integrations

Visual Studio Code

Use the 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:

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

:white_check_mark: Rules

:wrench: Indicates that the rule is fixable, and using --fix option on the command line can automatically fix some of the reported problems.
:bulb: Indicates that some problems reported by the rule are manually fixable by editor suggestions.
:star: Indicates that the rule is included in the plugin:svelte/recommended config.

Possible Errors

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

Rule ID	Description
svelte/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	disallow DOM manipulating
svelte/no-dupe-else-if-blocks	disallow duplicate conditions in {#if} / {:else if} chains	:star:
svelte/no-dupe-on-directives	disallow duplicate on: directives
svelte/no-dupe-style-properties	disallow duplicate style properties	:star:
svelte/no-dupe-use-directives	disallow duplicate use: directives
svelte/no-dynamic-slot-name	disallow dynamic slot name	:star::wrench:
svelte/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	disallow use of not function in event handler	:star:
svelte/no-object-in-text-mustaches	disallow objects in text mustache interpolation	:star:
svelte/no-reactive-reassign	disallow reassigning reactive values
svelte/no-shorthand-style-property-overrides	disallow shorthand style properties that override related longhand properties	:star:
svelte/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	disallow unknown style:property	:star:
svelte/require-store-callbacks-use-set-param	store callbacks must use set param
svelte/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	disallow warnings when compiling.	:star:
svelte/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	disallow use of {@html} to prevent XSS attack	:star:
svelte/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	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	disallow usage of button without an explicit type attribute
svelte/no-at-debug-tags	disallow the use of {@debug}	:star:
svelte/no-ignored-unsubscribe	disallow ignoring the unsubscribe method returned by the subscribe() on Svelte stores.
svelte/no-immutable-reactive-statements	disallow reactive statements that don't reference reactive values.
svelte/no-inline-styles	disallow attributes and directives that produce inline styles
svelte/no-reactive-functions	it's not necessary to define functions in reactive statements	:bulb:
svelte/no-reactive-literals	don't assign literal values in reactive statements	:bulb:
svelte/no-svelte-internal	svelte/internal will be removed in Svelte 6.
svelte/no-unused-class-name	disallow the use of a class in the template without a corresponding style
svelte/no-unused-svelte-ignore	disallow unused svelte-ignore comments	:star:
svelte/no-useless-mustaches	disallow unnecessary mustache interpolations	:wrench:
svelte/prefer-destructured-store-props	destructure values from object stores for better change tracking & fewer redraws	:bulb:
svelte/require-each-key	require keyed {#each} block
svelte/require-event-dispatcher-types	require type parameters for createEventDispatcher
svelte/require-optimized-style-attribute	require style attributes that can be optimized
svelte/require-stores-init	require initial value in store
svelte/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	derived store should use same variable names between values and callback
svelte/first-attribute-linebreak	enforce the location of first attribute	:wrench:
svelte/html-closing-bracket-spacing	require or disallow a space before tag's closing brackets	:wrench:
svelte/html-quotes	enforce quotes style of HTML attributes	:wrench:
svelte/html-self-closing	enforce self-closing style	:wrench:
svelte/indent	enforce consistent indentation	:wrench:
svelte/max-attributes-per-line	enforce the maximum number of attributes per line	:wrench:
svelte/mustache-spacing	enforce unified spacing in mustache	:wrench:
svelte/no-extra-reactive-curlies	disallow wrapping single reactive statements in curly braces	:bulb:
svelte/no-restricted-html-elements	disallow specific HTML elements
svelte/no-spaces-around-equal-signs-in-attribute	disallow spaces around equal signs in attribute	:wrench:
svelte/prefer-class-directive	require class directives instead of ternary expressions	:wrench:
svelte/prefer-style-directive	require style directives instead of style attribute	:wrench:
svelte/shorthand-attribute	enforce use of shorthand syntax in attribute	:wrench:
svelte/shorthand-directive	enforce use of shorthand syntax in directives	:wrench:
svelte/sort-attributes	enforce order of attributes	:wrench:
svelte/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	disallow variable or function declarations in nested blocks	:star:
svelte/no-trailing-spaces	disallow trailing whitespace at the end of lines	:wrench:

SvelteKit

These rules relate to SvelteKit and its best Practices.

Rule ID	Description
svelte/no-goto-without-base	disallow using goto() without the base path

Experimental

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

Rule ID	Description
svelte/experimental-require-slot-types	require slot type declaration using the $$Slots interface
svelte/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	support comment-directives in HTML template	:star:
svelte/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	This rule is no longer needed when using svelte-eslint-parser>=v0.19.0.

:beers: Contributing

Welcome contributing!

Please use GitHub's Issues/PRs.

See also CONTRIBUTING.md

Working With Rules

This plugin uses svelte-eslint-parser for the parser. Check here to find out about AST.

:lock: License

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