eslint-plugin-svelte3

An ESLint plugin for Svelte v3 components.

Features

• Compiler errors and warnings are displayed through ESLint
• Script blocks and template expression tags are linted with existing ESLint rules
• Svelte scope and stores are respected by unused variable and undefined variable rules
• Idioms like self-assignment and $: labels are always allowed, regardless of configuration

Requirements

• Svelte 3.2+
• ESLint 6+

Installation

Install the plugin package:

npm install --save-dev eslint-plugin-svelte3

Then add svelte3 to the plugins array in your .eslintrc.*, and set svelte3/svelte3 as the processor for your Svelte components.

For example:

1module.exports = {
2  parserOptions: {
3    ecmaVersion: 2019,
4    sourceType: 'module'
5  },
6  env: {
7    es6: true,
8    browser: true
9  },
10  plugins: [
11    'svelte3'
12  ],
13  overrides: [
14    {
15      files: ['*.svelte'],
16      processor: 'svelte3/svelte3'
17    }
18  ],
19  rules: {
20    // ...
21  },
22  settings: {
23    // ...
24  }
25};

By default, this plugin needs to be able to require('svelte/compiler'). If ESLint, this plugin, and Svelte are all installed locally in your project, this should not be a problem.

Interactions with other plugins

Care needs to be taken when using this plugin alongside others. Take a look at this list of things you need to watch out for.

Configuration

There are a few settings you can use to adjust this plugin's behavior. These go in the settings object in your ESLint configuration.

Passing a function as a value for a setting (which some of the settings below require) is only possible when using a CommonJS .eslintrc.js file, and not a JSON or YAML configuration file.

svelte3/ignore-warnings

This setting can be given a function that indicates whether to ignore a warning in the linting. The function will be passed a warning object and should return a boolean.

The default is to not ignore any warnings.

svelte3/compiler-options

Most compiler options do not affect the validity of compiled components, but a couple of them can. If you are compiling to custom elements, or for some other reason need to control how the plugin compiles the components it's linting, you can use this setting.

This setting can be given an object of compiler options.

The default is to compile with { generate: false }.

svelte3/ignore-styles

If you're using some sort of preprocessor on the component styles, then it's likely that when this plugin calls the Svelte compiler on your component, it will throw an exception. In a perfect world, this plugin would be able to apply the preprocessor to the component and then use source maps to translate any warnings back to the original source. In the current reality, however, you can instead simply disregard styles written in anything other than standard CSS. You won't get warnings about the styles from the linter, but your application will still use them (of course) and compiler warnings will still appear in your build logs.

This setting can be given a function that accepts an object of attributes on a <style> tag (like that passed to a Svelte preprocessor) and returns whether to ignore the style block for the purposes of linting.

The default is to not ignore any styles.

svelte3/named-blocks

When an ESLint processor processes a file, it is able to output named code blocks, which can each have their own linting configuration. When this setting is enabled, the code extracted from <script context='module'> tag, the <script> tag, and the template are respectively given the block names module.js, instance.js, and template.js.

This means that to override linting rules in Svelte components, you'd instead have to target **/*.svelte/*.js. But it also means that you can define an override targeting **/*.svelte/*_template.js for example, and that configuration will only apply to linting done on the templates in Svelte components.

The default is to not use named code blocks.

svelte3/compiler

In some esoteric setups, this plugin might not be able to find the correct instance of the Svelte compiler to use.

This setting can be given the result of require('.../path/to/svelte/compiler') to indicate which instance should be used in linting the components.

The default is require('svelte/compiler') from wherever the plugin is installed to.

svelte3/preprocess

You can use a preprocessor function to return custom AST info according to the original code.

For now this only supports module and instance scripts.

Using the CLI

It's probably a good idea to make sure you can lint from the command line before proceeding with configuring your editor.

Using this with the command line eslint tool shouldn't require any special actions. Just remember that if you are running eslint on a directory, you need to pass it the --ext flag to tell it which nonstandard file extensions you want to lint.

Integrations

See INTEGRATIONS.md for how to use this plugin with your text editor.

License

MIT