querySelector()，querySelectorAll()

//dom
<div id = 'box>
<div class = 'inner-box'></div>
<p class = 'inner-box'></p>
<div class = 'inner-box' id = 'operate-dom'></div>
</div>

//getDom    ------querySelector
var getDom = document.querySelector('#box');

//getDom   -----querySelectorAll()
var getDom = document.querySelectorAll('.innerbox');

//querySelectorAll('.innerbox') 返回来的是一个数组
var getDom = document.querySelectorAll('.innerbox');
console.log(getDom[1]);

//如p div 都带有同样的类名，下面是读出含有某一类名的p标签
var getDom = document.querySelectorAll('p.inner-box')