doctype html
meta charset="utf-8"
p createElement
button onclick="x()" 実行！
#target この前に要素を挿入しよう
javascript:
  function x(){
    var e=document.getElementById('target')
    var ne=document.createElement('p')
    ne.textContent=new Date().toLocaleTimeString()
    document.body.insertBefore(ne,e)
  }