//高效简洁                     //低消能
children　　　　　　　　　　　　        //childNodes
childElementCount            //childNodes.length
firstElementChild              //firstChild
lastEelmentChild              //lastChild
nextElementSibling           //nextSibling
previousElementSibling       //previousSibling

<div id="footer_bottom">
<a href="/AboutUS.aspx"></a><a href="/ContactUs.aspx">联系我们</a><a href="/about/ad.aspx">广告服务</a><a href="/about/job.aspx">人才服务</a>&copy;2006-2016 <a href="https://www.jb51.net/"></a>
</div>

var aArr1= document.querySelectorAll("#footer_bottom a");//简洁高效
var aArr2 = docuement.getElementById("footer_bottom").getElementsByTagName("a");//繁杂低效

//return 
<a href="/AboutUS.aspx"></a>,
<a href="/ContactUs.aspx">联系我们</a>,
<a href="/about/ad.aspx">广告服务</a>,
<a href="/about/job.aspx">人才服务</a>,

//选择第一个子节点
var a = document.querySelector("#footer_bottom a");
//return <a href="/AboutUS.aspx"></a>

//选择多个节点
var divs = document.querySelectorAll("div.footer,div.main,div.header");

var str = "nanananana";
for (var n = 0; n < str.length; n++) {}

　var str = "nanananana",
strLgth = str.length;
for (var n = 0; n < strLgth ; n++) {}

var coored = document.getElementById("ctgHotelTab");
document.getElementById("ctgHotelTab").style.top = coored.offsetTop + 35 + "px";

var coored = document.getElementById("ctgHotelTab"),
offetTop = coored.offsetTop + 35;
document.getElementById("ctgHotelTab").style.top = offetTop + "px";