一个用Ajax提交表单的代码 可以参考一下
<!-- 提交表单添加评论 -->
//增加一个POST或GET键值对 
function EssaySend(obj) {
var f = document.getElementById(obj);
var UserName = f.UserName.value;
var Email=f.Email.value;
var content=f.content.value;
var SoftID=f.SoftID.value;
var Grade=f.Grade.value;

if(UserName=="") {
window.alert("用户名不能为空。");
f.UserName.focus();
return
false;
}
if ((Email.indexOf("@") == -1) || (Email.indexOf(".") == -1)) 
{
alert("请查看您的E-mail地址是否正确,请重录入!");
f.Email.focus();
return(false);
}
if (content == "") 
{
alert("评论内容不能为空!");
f.content.focus();
return (false);
}
NeedLogin('添加商户');
//发送数据
inputdisabled(f);
var Temp="UserName=" + escape(UserName) + "&Email=" +escape(Email) + "&content=" + escape(content) + "&SoftID=" + escape(SoftID) + "&Grade=" + escape(Grade);
send_request("../writeessay.asp",Temp);
DialogHide();
}
//设置按钮为不可用
function inputdisabled(obj) 
{
for(var i=0;i<obj.elements.length;i++) 
{
obj.elements[i].disabled="disabled";
}
}
function gid(id)
{return document.getElementById?document.getElementById(id):null;}
function Browser()
{var ua, s, i;this.isIE = false;this.isNS = false;this.isOP = false;this.isSF = false;ua = navigator.userAgent.toLowerCase();s = "opera";if ((i = ua.indexOf(s)) >= 0){this.isOP = true;return;}s = "msie";if ((i = ua.indexOf(s)) >= 0) {this.isIE = true;return;}s = "netscape6/";if ((i = ua.indexOf(s)) >= 0) {this.isNS = true;return;}s = "gecko";if ((i = ua.indexOf(s)) >= 0) {this.isNS = true;return;}s = "safari";if ((i = ua.indexOf(s)) >= 0) {this.isSF = true;return;}}
function gname(name)
{return document.getElementsByTagName?document.getElementsByTagName(name):new Array()}
function StrCode(str)
{if(encodeURIComponent) return encodeURIComponent(str);if(escape) return escape(str);}
function ScreenConvert()
{var browser = new Browser();var objScreen = gid("ScreenOver");if(!objScreen) var objScreen = document.createElement("div");var oS = objScreen.style;objScreen.id = "ScreenOver";oS.display = "block";oS.top = oS.left = oS.margin = oS.padding = "0px";if (document.body.clientHeight) {var wh = document.body.clientHeight + "px";}else
if (window.innerHeight){var wh = window.innerHeight + "px";}else{var wh = "100%";}oS.width = "100%";oS.height = wh;oS.position = "absolute";oS.zIndex = "3";if ((!browser.isSF) && (!browser.isOP)){oS.background = "#cccccc";}else{oS.background = "#cccccc";}oS.filter = "alpha(opacity=40)";oS.opacity = 40/100;oS.MozOpacity = 40/100;document.body.appendChild(objScreen);var allselect = gname("select");for (var i=0; i<allselect.length; i++) allselect[i].style.visibility = "hidden";}
function DialogShow(showdata,ow,oh,w,h) 
{
var objDialog = document.getElementById("DialogMove");
if (!objDialog)
objDialog = document.createElement("div");
t_DiglogW = ow;t_DiglogH = oh;DialogLoc();
objDialog.id = "DialogMove";
var oS = objDialog.style;
oS.display = "block";
oS.top = t_DiglogY + "px";
oS.left = t_DiglogX + "px";
oS.margin = "0px";
oS.padding = "0px";
oS.width = w + "px";
oS.height = h + "px";
oS.position = "absolute";
oS.zIndex = "5";
oS.background = "#FFF";
oS.textAlign="center";
oS.fontSize="12px";
oS.paddingTop="5px";
oS.border = "1px dashed #CCCCCC";
objDialog.innerHTML = showdata;
document.body.appendChild(objDialog);
}
function DialogLoc(){var dde = document.documentElement;if (window.innerWidth){var ww = window.innerWidth;var wh = window.innerHeight;var bgX = window.pageXOffset;var bgY = window.pageYOffset;}else{var ww = dde.offsetWidth;var wh = dde.offsetHeight;var bgX = dde.scrollLeft;var bgY = dde.scrollTop;}t_DiglogX = (bgX + ((ww - t_DiglogW)/2));t_DiglogY = (bgY + ((wh - t_DiglogH)/2));}
function DialogHide(){ScreenClean();var objDialog = document.getElementById("DialogMove");if (objDialog) objDialog.style.display = "none";}
function ScreenConvert(){var browser = new Browser();var objScreen = gid("ScreenOver");if(!objScreen) var objScreen = document.createElement("div");var oS = objScreen.style;objScreen.id = "ScreenOver";oS.display = "block";oS.top = oS.left = oS.margin = oS.padding = "0px";if (document.body.clientHeight) {var wh = document.body.clientHeight + "px";}else
if (window.innerHeight){var wh = window.innerHeight + "px";}else{var wh = "100%";}oS.width = "100%";oS.height = wh;oS.position = "absolute";oS.zIndex = "3";if ((!browser.isSF) && (!browser.isOP)){oS.background = "#cccccc";}else{oS.background = "#cccccc";}oS.filter = "alpha(opacity=40)";oS.opacity = 40/100;oS.MozOpacity = 40/100;document.body.appendChild(objScreen);var allselect = gname("select");for (var i=0; i<allselect.length; i++) allselect[i].style.visibility = "hidden";}
function ScreenClean(){var objScreen = document.getElementById("ScreenOver");if (objScreen) objScreen.style.display = "none";var allselect = gname("select");for (var i=0; i<allselect.length; i++) allselect[i].style.visibility = "visible";}
function NeedLogin(Title) 
{
ScreenConvert();
var AJAX_LoginBody="<div id=\"DialogTitle\"> <img src=\"/show/img/Load.gif\" width=\"18\" height=\"18\" /> <br>评论正在写入中 <span id=\"AjaxMainCancle\" onclick=\"return DialogHide();\" style=\"cursor: pointer\">取消</span></div>";
DialogShow(AJAX_LoginBody,250,120,300,50);
}