cookie-contexts.js

function cookieContexts() {
    const iframes = Array.from(document.querySelectorAll('iframe'))

    const urls = iframes.map(iframe => iframe.src).filter(src =>  /https?:.+/.test(src))

    function uniq(a) {
        return a.sort().filter(function(item, pos, ary) {
            return !pos || item != ary[pos - 1];
        })
    }

    const hostnames = uniq(urls.map(url => new URL(url).hostname))
    return hostnames
}