<script type="text/javascript">
 function validateForm(){
    if(document.reply.title.value=http://www.mamicode.com/=""){//通过form名来获取form
  alert("please input the title!");
   document.reply.title.focus(();
     return false;
}
if(document.forms[0].cont.value=http://www.mamicode.com/=""){//通过forms数组获取form
alert("please input the content!");
document.reply.cont.focus();
return false;
}
return true;
}
<form name="reply" method="post" onsubmit="return validateForm();">
<input type="text" name="title" size="80"/><br/>
 <textarea name="cont" cols="80" rows="12"></textarea><br/>
<input type="submit" value=http://www.mamicode.com/"提交">
</form>

<script type="text/javascript">
function modifyItem(){
  if(trim(document.getElementById("itemName").value)==""){
alert("物料名称不能为空！");
document.getElementById("itemName").focus();
return;
}
with(document.getElementById("itemForm")){
 method="post";
 action="item.do?command=modify&pageNo=${itemForm.pageNo}";
submit();
}
}
//返回
function goBack(){
 window.self.location="item.do?command=list&pageNo=${itemForm.pageNo}";
}
</script>
<form name="itemForm" id="itemForm">
<input name="itemNo" type="text" id="itemNo" value=http://www.mamicode.com/"${item.itemNo}">
<input name="itemName" type="text" id="itemName" value=http://www.mamicode.com/"${item.itemName}">
<input name="btnModify" type="button" id="btnModify" value=http://www.mamicode.com/"修改" onclick="modifyItem()">
</form>