contenteditable

设置光标到内容最后

function setEndOfContenteditable(elem) {
  let sel = document.getSelection()
  sel.selectAllChildren(elem)
  sel.collapseToEnd()
  return sel
}

获取最后修改位置

function getLastEditRange() {
  let sel = document.getSelection()
  return sel.getRangeAt(0)
}