JAVAscript练习
firstChild & firstElementChildlastChild & lastElementChild
previousSibling & previousElementSiblingnextSibling & nextElementSibling
首尾子节点：firstChild & firstElementChild / lastChild & lastElementChild
兄弟子节点：previousSibling & previousElementSibling / nextSibling & nextElementSibling
兼容问题：都是通过判断来解决兼容问题