Answers for "how to add class susing dom"

vanilla javascript add class

document.addEventListener("DOMContentLoaded", function() {
  var faqContainers = document.getElementsByClassName('faq-container')
  var faqToggle = document.getElementsByTagName('body')[0]
  for (var i = 0; i < faqContainers.length; i++) {

    faqContainers[i].addEventListener('click', function() {
      if (faqToggle.classList.contains('faq-display')) {
        faqToggle.classList.remove('faq-display')
      } else {
        faqToggle.classList.add('faq-display')
      }
    })
  }
})

getelementsbyclassname add class

.newclassname {   border: 16px solid black; /* Light grey */
  border-top: 16px solid black; /* Blue */
  border-radius: 50%;
  width: 120px;
  height: 120px;
  animation: spin 2s linear infinite; }
  @keyframes spin {
0% { transform: rotate(0deg); }
100% { transform: rotate(360deg); }
}