.eslintrc.js

/* eslint-env node */
module.exports = {
  plugins: ['@typescript-eslint', 'svelte3'],
  extends: [
    'eslint:recommended',
    // 'plugin:@typescript-eslint/recommended',
    // 'plugin:@typescript-eslint/recommended-requiring-type-checking',
  ],
  parser: '@typescript-eslint/parser', // add the TypeScript parser
  parserOptions: {
    ecmaVersion: 2020,
    sourceType: 'module',
    tsconfigRootDir: __dirname,
    project: ['./tsconfig.eslint.json'],
    extraFileExtensions: ['.svelte'],
  },
  env: {
    node: true,
    es6: true,
    browser: true,
    jest: true,
  },
  overrides: [
    {
      // see https://github.com/sveltejs/eslint-plugin-svelte3/blob/master/OTHER_PLUGINS.md
      files: ['*.svelte'],
      processor: 'svelte3/svelte3',
      rules: {
        'import/first': 'off',
        'import/no-duplicates': 'off',
        'import/no-mutable-exports': 'off',
        'import/no-unresolved': 'off',
      },
    },
    {
      files: ['*.ts'],
      extends: [
        'eslint:recommended',
        'plugin:@typescript-eslint/recommended',
        'plugin:@typescript-eslint/recommended-requiring-type-checking',
      ],
      rules: {
        '@typescript-eslint/no-non-null-assertion': 'off',
        '@typescript-eslint/no-unnecessary-type-assertion': 'off', // generate as a bunch of false positives
      },
    },
  ],
  settings: {
    'svelte3/typescript': require('typescript'), // pass the TypeScript package to the Svelte plugin
    // ...
  },
};