.eslintrc.js

// https://github.com/typescript-eslint/typescript-eslint/blob/master/docs/getting-started/linting/README.md#getting-started---linting-your-typescript-codebase

module.exports = {
  root: true,
  parser: "@typescript-eslint/parser",
  plugins: ["@typescript-eslint", "eslint-plugin-prettier", "jest"],
  extends: [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
    "plugin:prettier/recommended",
    "plugin:jest/recommended",
  ],
  rules: {
    "prettier/prettier": "error",
    "@typescript-eslint/explicit-module-boundary-types": "error",
    "no-param-reassign": "error",
  },
  overrides: [
    // {
    //   files: ["test/**/*.ts", "**/?(*.)+(spec|test).+(ts|tsx|js)"],
    //   rules: {
    //     // "no-param-reassign": "off",
    //   },
    // },
    {
      files: ["*.js"],
      rules: {
        "no-undef": "off",
        "@typescript-eslint/no-var-requires": "off",
      },
    },
    {
      files: ["*.test.ts", "*.spec.ts"],
      rules: {
        "jest/no-conditional-expect": "off",
        "@typescript-eslint/no-non-null-assertion": "off",
      },
    },
    //
  ],
};