<script type="text/javascript">
   var flag=Request("y_name");
    if(flag!=null && flag!="")
  {  
     if(flag=="cl")
     {
       document.getElementById("clxt").className="affairlab1";
       document.getElementById("gdxt").className="affairlab2";
       document.getElementById("zhjkxt").className="affairlab2";
       document.getElementById("gdaoxt").className="affairlab2";
       document.getElementById("pbmxt").className="affairlab2";
       document.getElementById("sjpxt").className="affairlab2";
       document.getElementById("sdtfxt").className="affairlab2";
       document.getElementById("xhxt").className="affairlab2";
       document.getElementById("txxt").className="affairlab2";
       document.getElementById("dtxt").className="affairlab2";
       document.getElementById("zdftxt").className="affairlab2";
     
     }
     else if(flag=="gd")
     {
       document.getElementById("clxt").className="affairlab2";
       document.getElementById("gdxt").className="affairlab1";
       document.getElementById("zhjkxt").className="affairlab2";
       document.getElementById("gdaoxt").className="affairlab2";
       document.getElementById("pbmxt").className="affairlab2";
       document.getElementById("sjpxt").className="affairlab2";
       document.getElementById("sdtfxt").className="affairlab2";
       document.getElementById("xhxt").className="affairlab2";
       document.getElementById("txxt").className="affairlab2";
       document.getElementById("dtxt").className="affairlab2";
       document.getElementById("zdftxt").className="affairlab2";
     
     }
        else if(flag=="pbm")
     {
       document.getElementById("clxt").className="affairlab2";
       document.getElementById("gdxt").className="affairlab2";
       document.getElementById("zhjkxt").className="affairlab2";
       document.getElementById("gdaoxt").className="affairlab2";
       document.getElementById("pbmxt").className="affairlab1";
       document.getElementById("sjpxt").className="affairlab2";
       document.getElementById("sdtfxt").className="affairlab2";
       document.getElementById("xhxt").className="affairlab2";
       document.getElementById("txxt").className="affairlab2";
       document.getElementById("dtxt").className="affairlab2";
       document.getElementById("zdftxt").className="affairlab2";
     
     }
      else if(flag=="sjp")
     {
       document.getElementById("clxt").className="affairlab2";
       document.getElementById("gdxt").className="affairlab2";
       document.getElementById("zhjkxt").className="affairlab2";
       document.getElementById("gdaoxt").className="affairlab2";
       document.getElementById("pbmxt").className="affairlab2";
       document.getElementById("sjpxt").className="affairlab1";
       document.getElementById("sdtfxt").className="affairlab2";
       document.getElementById("xhxt").className="affairlab2";
       document.getElementById("txxt").className="affairlab2";
       document.getElementById("dtxt").className="affairlab2";
       document.getElementById("zdftxt").className="affairlab2";
     }
 </script>
   我加了这段代码后 在页面的左下角 就报 错误‘document.getElementById(...)'为空或不是对象。但是又确实存在这些对象,而且ID都是对的     

解决方案 »

  1.   

    把这段代码放到最后

    <script type="text/javascript" defer>
      

  2.   

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>无标题页</title>
        <style type="text/css">
        body
        {
            font-family:"宋体";
            font-size:12px;
        }
        </style>
        <script language="javascript" type="text/javascript">
        document.getElementById("divTest").innerHTML="Hello World";
        //页面加载完这段javascript代码的时候,就开始运行了,但是,下面的id为divTest div标签还未加载,所以找不到它
        </script>
    </head>
    <body>
        <div id="divTest">
        </div>
    </body>
    </html>
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>无标题页</title>
        <style type="text/css">
        body
        {
            font-family:"宋体";
            font-size:12px;
        }
        </style>
    </head>
    <body>
        <div id="divTest">
        </div>
        <script language="javascript" type="text/javascript">
        document.getElementById("divTest").innerHTML="Hello World";
        //把这段代码移到divTest的下面,加载完divTest标签后,再执行document.getElementById("divTest")就找到了
        </script>
    </body>
    </html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>无标题页</title>
        <style type="text/css">
        body
        {
            font-family:"宋体";
            font-size:12px;
        }
        </style>
        <script language="javascript" type="text/javascript">
        window.onload=function()
        {
            document.getElementById("divTest").innerHTML="Hello World";
            // 不过,最佳建议,是你把一些初始化代码放到window.onload中,页面加载所有内容后,再开始运行,这样就没有问题了
        }
        </script>
    </head>
    <body>
        <div id="divTest">
        </div>
    </body>
    </html>
      

  3.   

    类似代码:
    document.getElementById("对象ID").className="affairlab2"; 应该是没有错的,不过JavaScript是大小写敏感,所以你仔细检查看是否无意中有写错的,如下获取参数值在JavaScript中是否有问题?感觉是不对....:
    var flag=Request("y_name"); 
      

  4.   

    哦,对了,web页面是顺序执行...所以代码应该放到页面的尾部...学习了,呵呵
      

  5.   

    lihai a   niu cha a