<div class="left"><img src="img/123.jpg"/></div>
<div class="left"><img src="img/345.jpg"/></div>
</div>
////////////////
var divs=ddd.getElementsByTagName("div")
divs[0].style.marginRight = "20px"
divs[1].style.marginLeft = "20px"
<meta charset="utf-8" /><style>
a{color: #fff}
ul, ol, li {
list-style:none outside none
padding: 0
margin: 0
}
#list{
width: 430px
overflow: hidden
background: #cecece
}
#list li{
width: 100px
float: left
margin-right: 10px
margin-bottom: 20px
background: #333
}
</style>
<ul id="list">
<li><a href="#">1</a></li>
<li><a href="#">2</a></li>
<li><a href="#">3</a></li>
<li><a href="#">4</a></li>
<li><a href="#">5</a></li>
<li><a href="#">6</a></li>
<li><a href="#">7</a></li>
<li><a href="#">8</a></li>
<li><a href="#">9</a></li>
<li><a href="#">10</a></li>
<li><a href="#">11</a></li>
<li><a href="#">12</a></li>
<li><a href="#">13</a></li>
</ul>
<script>
function del4margin(x) {
var ObjLi = document.getElementById("list").getElementsByTagName("li")
for (var i = 1 i < ObjLi.length i++) {
if (i % x == 0 && i !== 0) {
ObjLi[i-1].style.background = "red"
ObjLi[i-1].style.marginRight = "0"
}
}
}
window.onload = del4margin(4) //传入参数4,去掉第4个li的外边距
</script>