帮帮忙一个很容易的JS问题 在线等 急

Question

<td align="center" nowrap>
        <select name="projectId" id="_projectId" onchange = "selectProjectId()" >
<option selected="true">产品/项目名称</option>
<option value="all">全部</option>
 <% 
 if(projects!=null){
 for(int i= 0;i<projects.size();i++){
PaProjectVO vo = (PaProjectVO)projects.get(i);
%>
<option value="<%= vo.getProjectId()%>">
<%= vo.getProjectName() %>
</option>
<%}}%>
        </select>
        </td>
function selectProjectId(){
 
var _projectId=document.getElementById("_projectId").value; 
if(_projectId=="all"){
window.location="<%= contextpath%>/servlet/GetPromisesResultServlet ";
}       
else{
window.location="<%= contextpath%>/servlet/GetPromisesResultServlet?_projectId="+_projectId;  
}
}System.out.print("canshu resultType==="+resultType);
            String projectId = request.getParameter("_projectId");为什么 _projectId 一直取不到 输出 一直为空 <%= vo.getProjectName() %>
已经正常输出  是我函数里面有错还是 select里面有错  
vo.getProjectId()正常应该输出为Integer 那边servlet 也是根据request.getParemeter("_projectId")的值来查询,现在关键是request.getParemeter("_projectId")一直为NULL  哪位朋友知道 非常感谢

Answer 1

<select name="projectId" id="_projectId" onchange = "selectProjectId()" >var _projectId=document.getElementById("_projectId").value; _projectId元素中要有value属性才可以取到document.getElementById("_projectId").value;<select name="projectId" id="_projectId" onchange = "selectProjectId()" value="hejunbin" >

Answer 2

var _projectId=document.getElementById("_projectId").value;
改成
var objProject=document.getElementById("_projectId");
var _projectId=objProject.option[objProject.selectedIndex].value;
试试看

Answer 3

request.getParemeter("_projectId")这样取当然为null,
_projectId是id,改为request.getParameter("projectId")