function getEls(container) {
    const elems = container.querySelectorAll("*");
    console.log(elems.length);
    for (let i = 0, ii = elems.length; i < ii; i++) {
        const elem = elems[i];
        const ln = elem.localName;
        if (ln.indexOf('-') > -1) {
            if (customElements.get(ln)) {
                console.log(ln);
            }
        }else if(ln === 'iframe'){
            try{
                getEls((<any> elem).contentWindow.document.body);
            }catch(e){}
        }
    }
}
getEls(document.body)