剑指前端（前端入门笔记系列）——DOM（元素节点）

<div id="box">div_id_1</div>
<div id="box">div_id_2</div>
<div id="char">div_id_2</div>
 
<div class="cont">div_class_1</div>
<div class="cont">dic_class_2</div>
<div class="pre">dic_class_2</div>
 
<span>span1</span>
<span>span2</span>
 
<input type="text" name="user" id="user2" value="user2" />
<input type="text" name="user" id="user1" value="user1" />
<input type="text" name="pass" id="user" value="pass" />
<script type="text/javascript">
    //id:返回的是单个元素，就算有多个，获得的也只是一个
    var oBox = document.getElementById("box"<div id="box">div_id_1</