snippet.js

(function(){
    let list=document.querySelectorAll('.event--vote-stars');
    let score = 0;
    for (let i=0,l=list.length;i<l;i++) {
        let el=list[i];
        score+=el.querySelectorAll('a.star.is-selected').length;
    }
    console.info(score/list.length);
})();