1. Go to event page
2. click invite > invite friends
3. Scroll to bottom. Scroll ALL the way down until names stop loading
4. Past script to URL . (on chrome you should paste script without "javascript:", and after paste add "javascript:" )

javascript:elms=document.getElementsByName("profileChooserItems")[0];var tmpElms = [];var tmpElmsObj = {};elmsClass=document.getElementsByClassName('_1pu0');for (i=0;i<elmsClass.length;i++){var id = elmsClass[i].getAttribute("data-reactid");var classActive = elmsClass[i].getElementsByClassName('_1pu2')[0];id = classActive.getAttribute("aria-labelledby");classActive.className = "_1pu2 _1pu3";classActive.setAttribute('aria-checked', true);id = id.split('-');id = id[0];tmpElmsObj[id] = 1;tmpElms.push(id);}document.getElementsByName('profileChooserItems')[0].value=JSON.stringify(tmpElmsObj);void(0);

5. click enter