get-etld

Returns the effective top-level domain (eTLD) corresponding to the current web page without the use of a public suffix list.

Because of the methodology used, this library is very small.

What's an effective top-level domain (eTLD)?

When someone purchases a domain, the domain always ends in an existing effective top-level domain (eTLD). For example, if you purchase example.com, the eTLD is com. Usually the eTLD is what comes after the last period, but not always. If you purchase example.co.uk, for example, co.uk is the eTLD. No websites or services are hosted on eTLDs; they only serve as the basis for domains that consumers can register.

Requirements

This will only work in a browser and cookies must be enabled.

How detection is accomplished

There are no consistent, logical rules whereby the effective top-level domain can be parsed from a hostname. Instead, the Public Suffix List is a publicly curated list of all known effective top-level domains. Ths list changes over time. The only way to parse the effective top-level domain from a hostname is by comparing the ending of the hostname to the Public Suffix List.

The Public Suffix List is very large, making it prohibitive to load into a browser. Fortunately, there's a second-hand way of accessing this list.

As it turns out, browsers use this list to determine which domains can accept cookies. For example, browsers allow store.example.co.uk to set cookies for store.example.co.uk and example.co.uk, but not co.uk or uk, because co.uk and uk are both on the Public Suffix List.

Because of this, we can determine the top-level domain by attempting to write a cookie on uk, then co.uk, then example.co.uk, then store.example.co.uk, until we succeed in writing a cookie. In this case, the first attempt that will succeed is example.co.uk. By removing the first segment (example), we arrive at co.uk, the effective top-level domain.

Installation

If you use npm for package management, you can install get-etld by running the following command from within your project's directory:

npm install get-etld

Usage

import getEtld from "get-etld";

console.log(getEtld());

If cookies are not enabled, an error will be thrown.

If the hostname is localhost, the eTLD will be localhost.

Special Recognition

Full credit goes to Joe Khoury for devising the strategy used to determine the apex domain.