eslint.config.js

import globals from 'globals'
import tsParser from '@typescript-eslint/parser'
import parser from 'svelte-eslint-parser'
import path from 'node:path'
import { fileURLToPath } from 'node:url'
import js from '@eslint/js'
import { FlatCompat } from '@eslint/eslintrc'
import { includeIgnoreFile } from '@eslint/compat'

const __filename = fileURLToPath(import.meta.url)
const __dirname = path.dirname(__filename)
const compat = new FlatCompat({
  baseDirectory: __dirname,
  recommendedConfig: js.configs.recommended,
  allConfig: js.configs.all
})
const gitignorePath = path.resolve(__dirname, '.gitignore')

export default [
  ...compat.extends(
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended',
    'plugin:svelte/recommended',
    'prettier'
  ),
  includeIgnoreFile(gitignorePath),
  {
    languageOptions: {
      globals: {
        ...globals.browser,
        ...globals.node,
        ...globals.mocha
      },

      parser: tsParser,
      ecmaVersion: 2019,
      sourceType: 'module',

      parserOptions: {
        extraFileExtensions: ['.svelte']
      }
    },

    rules: {
      'consistent-return': [
        'warn',
        {
          treatUndefinedAsUnspecified: false
        }
      ]
    }
  },
  {
    files: ['**/*.svelte'],

    languageOptions: {
      parser: parser,
      ecmaVersion: 5,
      sourceType: 'script',

      parserOptions: {
        parser: '@typescript-eslint/parser'
      }
    }
  }
]