节点的操作

• appendChild(节点)-添加

let oul = document.getElementsByTagName("ul")[0];
let newOli = document.createElement("li");
oul.appendChild(newOli);
//在oul下的末尾添加一个newOli的节点

• insertBefore(要插入的节点，参照点)-插入

let oul = document.getElementsByTagName("ul")[0];
let newOli = document.createElement("li");
oul.insertBefore(newOli, oul.children[2]);
//在oul下把newOli插入到第二个节点之前

• replaceChild(要插入的节点，参照点)-替换

let oul = document.getElementsByTagName("ul")[0];
let newOli = document.createElement("li");
oul.replaceChild(newOli, oul.children[2]);
//在oul下用newOli替换掉第二个节点

• removerChild(要删除的节点)-删除

let oul = document.getElementsByTagName("ul")[0];
oul.removeChild(oul.children[2]);
//在oul下删除第二个节点

• cloneNode(flag)-复制

let oul = document.getElementsByTagName("ul")[0];
let newOli = oul.children[2].cloneNode(true);
let newOli1 = oul.children[2].cloneNode(false);
//复制oul下的第二个节点,true为深复制、false为浅复制