<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
</head>
<body>
<ul class="ul1" id="ul1">
<li>1111111</li>
<li class="box box">1111111</li>
<li>1111111</li>
<li class="box box1">1111111</li>
</ul>
<ul class="ul2" id="ul2">
<li>1111111</li>
<li class="box box">1111111</li>
<li>1111111</li>
<li class="box box1">1111111</li>
</ul>
<div id="p1">
<p class="box">fsdfsdfsd</p>
</div>
<script>
var oul=document.getElementById('ul1');
var odiv=getByClass(oul,'box');
console.log(odiv);
for(var i=0;i<odiv.length;i++){
odiv[i].style.background='red';
}
function getByClass(oparent,classna){
var a=oparent.getElementsByTagName('*');
var result=[];
for(var i=0;i<a.length;i++){
var arr=a[i].className.split(' ');
for(var j=0;j<arr.length;j++){
if(arr[j]==classna){
result.push(a[i]);
break;
}
}
}
return result;
}
</script>
</body>
</html>