php+ajax实现文章自动保存的方法

if(sec>0) {
       autosavetimer = setTimeout("autosavetime("+sec+"-1)",1000);　　
     //这里就是如果当sec>0的时候，第一秒执行一次autosavetime这个函数，同时会把sec-1的值写入autosavetimebox中
}else {
          var title=document.getElementById('title');
          if(title.value!=''){
                                  autosave_post();
          }else{
                 document.getElementById('autosavetimebox').innerHTML='不用保存';   
          }
}

var userAgent = navigator.userAgent.toLowerCase();
var is_opera  = (userAgent.indexOf('opera') != -1);
var is_saf    = ((userAgent.indexOf('applewebkit') != -1) || (navigator.vendor == 'Apple Computer, Inc.'));
var is_webtv  = (userAgent.indexOf('webtv') != -1);
var is_ie     = ((userAgent.indexOf('msie') != -1) && (!is_opera) && (!is_saf) && (!is_webtv));
var is_ie4    = ((is_ie) && (userAgent.indexOf('msie 4.') != -1));
var is_moz    = ((navigator.product == 'Gecko') && (!is_saf));
var is_kon    = (userAgent.indexOf('konqueror') != -1);
var is_ns     = ((userAgent.indexOf('compatible') == -1) && (userAgent.indexOf('mozilla') != -1) && (!is_opera) && (!is_webtv) && (!is_saf));
var is_ns4    = ((is_ns) && (parseInt(navigator.appVersion) == 4));
var is_mac    = (userAgent.indexOf('mac') != -1);
if ((is_ie & !is_ie4) || is_moz || is_saf || is_opera)
{
    var allowajax=1;
}else{
    var allowajax=0;
}
var xmlHttp = false;
function makeSendData(postData,url,functionName,httptype) {
 
var posturl=url;
try {
   xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
   try {
     xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
   } catch (e2) {
     xmlHttp = false;
   }
}
if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
   xmlHttp = new XMLHttpRequest();
}
 
if (!xmlHttp) {
        alert('Cannot send an XMLHTTP request');
        return false;
}
 
// 提交表单的方式
xmlHttp.open(httptype, posturl, true);
 
// 当表单提交完成后触发一个事件
var changefunc="xmlHttp.onreadystatechange = "+functionName;  ///////from bob
eval (changefunc);
xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded'); 
xmlHttp.send(postData);
}
function autosave_post()
{
    var title=document.getElementById('title').value;
    var content = window.frames["Editor"].window.frames["HtmlEditor"].document.getElementsByTagName("BODY")[0].innerHTML;
    var postTime=document.getElementById('postTime').value;
    if(allowajax==1)
    {
        content=postencode(content);
        title=postencode(title);
        var post="title="+title+"&content="+content+"&postTime="+postTime+"";
        var url="ajax.php?act=autosave";
        makeSendData(post,url,'autosave','POST');
    }
}
function autosave()
{
    if(xmlHttp.readyState == 4)
    {
        if(xmlHttp.status == 200)
        {
            var autoresponse=xmlHttp.responseText;
            var automessage=document.getElementById('autosavetimebox');
            if(autoresponse.indexOf("<autosave_error>")!=-1)
            {
                automessage.innerHTML='您还没有添写信息，不用保存草稿';
                return false;
            }
            if(autoresponse.indexOf("<autosave_ok>")!=-1)
            {
                automessage.innerHTML='保存成功，您可以在发生意外的时候载入草稿';
                finddraft();
            }
        }
    }
}
function finddraft()
{
    if(allowajax==1)
    {
        var url="ajax.php?act=loaddraft";
        makeSendData(null,url,'loaddraft','POST');
    }
}
function loaddraft()
{
    var draftbox=document.getElementById('draft');
    if(xmlHttp.readyState < 4)
    {
        draftbox.innerHTML='草稿载入中...';
    }
    if(xmlHttp.readyState == 4)
    {
        if(xmlHttp.status == 200)
        {
            draftbox.innerHTML=xmlHttp.responseText;
        }
    }
}
function cleardraft()
{
    if(allowajax==1)
    {
        var url="ajax.php?act=cleardraft";
        makeSendData(null,url,'nodraft','POST');
    }
}
function nodraft()
{
    var draftbox=document.getElementById('draft');
    if(xmlHttp.readyState < 4)
    {
        draftbox.innerHTML='载入中...';
    }
    if(xmlHttp.readyState == 4)
    {
        if(xmlHttp.status == 200)
        {
            draftbox.innerHTML=xmlHttp.responseText;
        }
    }
}
//encode string
function postencode (str) { 
    str=encodeURIComponent(str);
    if (is_moz) str=str.replace(/%0A/g, "%0D%0A"); //from bob
    return str;
}

var autosavetimer;
function autosavetime(sec) {
   clearTimeout(autosavetimer);
   document.getElementById('autosavetimebox').innerHTML=sec+"秒";
   if(sec>0) {
       autosavetimer = setTimeout("autosavetime("+sec+"-1)",1000);
   }else {
       var blogtitle=document.getElementById('title');
       if(blogtitle.value!=''){
           autosave_post();
       }else{
           document.getElementById('autosavetimebox').innerHTML='不用保存';  
       }
   }
}
function startimer()
{
    var starttime=document.getElementById('autosavetimebox').innerHTML;
    if(starttime=='保存成功，您可以在发生意外的时候载入草稿' || starttime=='您还没有添写信息，不用保存草稿')
    {
        starttime='60';
    }else{
        starttime=starttime.replace('秒','');
    }
    var autosavefunbox=document.getElementById('autosavefunbox');
    autosavefunbox.innerHTML='<a href="javascript教程:" onClick="javascript：stoptimer()">停止计时</a>';
    starttime==0 ? starttime=60 : starttime=starttime;
    autosavetime(starttime);
}
function stoptimer()
{
    var autosavefunbox=document.getElementById('autosavefunbox');
    autosavefunbox.innerHTML='<a href="javascript：" onClick="javascript：startimer()">开始计时</a>';
    clearTimeout(autosavetimer);
}