5 star solution

    function setup() {
      let ratingContainer = document.getElementById('rating');

      function resetRatings(){
        for(let i = 0; i < ratingContainer.children.length; i++){
            ratingContainer.children[i].classList = [];
          }
      }

      ratingContainer.addEventListener('click', (e) => {
        if(e.target.tagName === 'SPAN'){
          resetRatings();
          let ratingContainerArray = [].slice.call(ratingContainer.children);
          let starIndex = ratingContainerArray.indexOf(e.target);

          for(let i = 0; i <= starIndex; i++){
            ratingContainer.children[i].classList.add('active');
          }
        }
      })
    }

    // Example case.
    document.body.innerHTML = `
    <div id='rating'>
      <span>*</span>
      <span>*</span>
      <span>*</span>
      <span>*</span>
      <span>*</span>
    </div>`;

    setup();

    document.getElementsByTagName("span")[2].click();
    console.log(document.body.innerHTML);