doctype html
meta charset="utf-8"
p ネイティブ関数で点滅
.tgt
.tgt
.tgt
css:
  .tgt {
    width:300px;height:100px;
    background-color:yellow;margin:20px
  }
javascript:
  var n=0
  var es=document.querySelectorAll('.tgt')
  setInterval(()=>{
    n+=1
    es.forEach(e=>e.style.opacity=[0,100][n%2])
  },2000)