【javascript】下拉列表select 由左边框移动到右边

来源：互联网发布：mac安装jdk1.8 编辑：程序博客网时间：2024/04/30 04:27

当页面还没有加载完的时候调用下面语句，会取不到“add” 这个对象，提示为空或不是对象

document.getElementById("add").onclick = function(){ alert("hello"); }

当使用便可取的对象

  window.onload = function(){ document.getElementById("add").onclick = function(){ alert("hello"); } }

<script type="text/javascript">//选中的从左边移到右边  function toright() { var firstElement = document.getElementById("first"); var secondElement = document.getElementById("second"); var firstoptionElement = firstElement.getElementsByTagName("option"); var len = firstoptionElement.length; for(var i=0;i<len;i++){if(firstElement.selectedIndex != -1){ //selectedIndex 是select 的属性 secondElement.appendChild(firstoptionElement[firstElement.selectedIndex]); } }} //全部移动到右边 function allright(){  var firstElement = document.getElementById("first"); var secondElement = document.getElementById("second"); var firstoptionElement = firstElement.getElementsByTagName("option"); var len = firstoptionElement.length; for(var i=0;i<len;i++){ secondElement.appendChild(firstoptionElement[0]);//option选项选中时候索引为0  } } //双击移动到右边 function db(){/* //方法一 var firstElement = document.getElementById("first"); var secondElement = document.getElementById("second"); var firstoptionElement = firstElement.getElementsByTagName("option"); var len = firstoptionElement.length; for(var i=0;i<len;i++){if(firstElement.selectedIndex != -1){ //selectedIndex 是select 的属性 secondElement.appendChild(firstoptionElement[firstElement.selectedIndex]); } } *///方法二var firstElement = document.getElementById("first"); var secondElement = document.getElementById("second"); secondElement.appendChild(firstElement[firstElement.selectedIndex]); } </script><style type="text/css"> </style></head><body>   <table width="285" height="169" border="0" align="left">    <tr>    <td width="126">    <select name="first" size="10" multiple="multiple" id="first" ondblclick="db()">    <option value="1">选项1</option>    <option value="2">选项2</option>    <option value="3">选项3</option>    <option value="4">选项4</option>    <option value="5">选项5</option>    <option value="6">选项6</option>    </select>    </td>    <td width="69" valign="middle">    <input id="add" name="add" type="button" value="---->" onclick="toright()"/>    <input id="add_all" name="add_all" type="button" value="==>" onclick="allright()"/>    </td>    <td width="127" align="left">    <select name="second" size="10" multiple="multiple" id="second">    <option value="选项8">选项8</option>    </select>    </td>    </tr>   </table></body>