<div class="aaa1">
<div class="">123</div>
<span>2222</span>
</div>
var aa=document.getElementsByClassName("aaa1")[0].children[1].innerHTML
console.log(aa);
<div class="aaa1">
<div class="">123</div>
<span>2222</span>
</div>
var aa=document.getElementsByClassName("aaa1")[0].children[1].innerHTML
console.log(aa);