js获取选中的单选按钮的值

1、页面

<table cellspacing="0" cellpadding="4" width="100%" align="center" border="0" class="table_title">
						
						<tr>
							<th width="5%">
								选择
							</th>
							<th width="20%">
								文件名
							</th>
							<th width="20%">
								大小
							</th>
							<th width="30%">
								操作
							</th>
						</tr>

						<%
								for(int i=0;i<bakfileSize;i++){
									DataFile dataFile = (DataFile)bakfileList.get(i);
									String fileName = dataFile.getFileName();
									long fileSize = dataFile.getFileSize();
						%>
						<tr id="" onMouseOver="changeColor(this,1)" onmouseout="changeColor(this,2)">
							<td>
								<input type="radio" name="itemradio" value="<%=fileName%>" />
							</td>
							<td>
								<%=fileName%> 
							</td>
							<td>
								<%=fileSize%> KB
							</td>
							<td> 
								<a href="delBakFile.jsp?file_name=<%=fileName%>">删除</a>
							</td>
						</tr>
						<%}%>
						<tr>
							<th colspan="4" align="center">
								<input type="button" value="开始还原数据" class="submitButton" onclick="restore()"/>
							</th>
						</tr>
					</table>

2、js

function restore(){//恢复数据库,每次只能恢复一个文件
 
			    var itemradio = document.getElementsByName("itemradio"); 
			    var itemvalue = '';  
			    for(i=0;i<itemradio.length;i++)   
			    {   
			      	if(itemradio[i].checked){
			      		itemvalue = itemradio[i].value;
			      	}
			  	} 
			  	if(itemvalue==''){
			  		alert('请选择备份的数据库！');
			  		return false;
			  	}  
				document.getElementById('backup_dbname').value = itemvalue;
				document.submitForm.submit();
			}