RocketChat/Rocket.Chat

export const getBaseURI = (): string => {
    if (document.baseURI) {
        return document.baseURI;
    }

    // Should be exactly one tag:
    //   https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
    const base = document.getElementsByTagName('base');

    // Return location from BASE tag.
    if (base.length > 0) {
        return base[0].href;
    }

    // Else use implementation of documentURI:
    //   http://www.w3.org/TR/DOM-Level-3-Core/core.html#Node3-baseURI
    return document.URL;
};

export const isExternal = (href: string): boolean => href.indexOf(getBaseURI()) !== 0;