ele.js

// 1
const uls = document.getElementByTagName('ul')
for(u of uls) {
  u.classList.add('bar')
}


// 2
document.querySelector('#list > li:nth-child(10)').remove()

// 3
const list = document.getElementById('list')
const child = document.querySelector('#list > li:nth-child(500)')
if (child) {
  const next = child.nextSibling

  const element = document.createElement('li')
  element.innerText = '<v2ex.com />'

  if (next) {
    list.insertBefore(element, next)
  } else {
    list.appendChild(element)
  }
}

// 4
const list = document.getElementById('list')
list.addEventListener('click', function(e) {
  let target = e.target
  let last = target.closest('#list > li')
  /* while (target.id !== 'list') {
    last = target
    target = target.parentNode
  } */

  let i = 1;
  while (last = last.previousSibling) {
    if (last.nodeType === 1) { ++i }
  }
  alert(i)
}, false)

getElementsByTagName 落下s 😄