For explanation purpose on DefinitelyTyped/DefinitelyTyped#28890

README.md

For discussions on DefinitelyTyped/DefinitelyTyped/pull/28890

1. Install dependencies

$ npm install

2. Compile index.ts and you'll see no error.

$ npm run tsc index.ts

index.ts

const x: ValidatorJS.IsFQDNOptions = {
  require_tld: true,
  allow_underscores: true,
  allow_trailing_dot: true
};

package-lock.json

{
  "name": "validatorjs-types-considerations",
  "version": "0.0.0",
  "lockfileVersion": 1,
  "requires": true,
  "dependencies": {
    "@types/validator": {
      "version": "9.4.2",
      "resolved": "https://registry.npmjs.org/@types/validator/-/validator-9.4.2.tgz",
      "integrity": "sha512-v6H2QH+oXVdLKp9keOJi5LQSt6X5/XIOtK1YmbCzvkAT2kHW9WyQkixit9w1UgJpBGrDCqqCZlQ+Qucpmsf8hA==",
      "dev": true
    },
    "typescript": {
      "version": "3.0.3",
      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.0.3.tgz",
      "integrity": "sha512-kk80vLW9iGtjMnIv11qyxLqZm20UklzuR2tL0QAnDIygIUIemcZMxlMWudl9OOt76H3ntVzcTiddQ1/pAAJMYg==",
      "dev": true
    },
    "validator": {
      "version": "10.7.1",
      "resolved": "https://registry.npmjs.org/validator/-/validator-10.7.1.tgz",
      "integrity": "sha512-tbB5JrTczfeHKLw3PnFRzGFlF1xUAwSgXEDb66EuX1ffCirspYpDEZo3Vc9j38gPdL4JKrDc5UPFfgYiw1IWRQ=="
    }
  }
}

package.json

{
  "name": "validatorjs-types-considerations",
  "version": "0.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "tsc": "./node_modules/.bin/tsc",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Naoto Yokoyama",
  "license": "MIT",
  "dependencies": {
    "validator": "^10.7.1"
  },
  "devDependencies": {
    "@types/validator": "^9.4.2",
    "typescript": "^3.0.3"
  }
}