PHP ajax

1.取得XMLHttpRequest对象
function GetXmlHttpObject()
{
var xmlHttp=null;
try
{
// Firefox, Opera 8.0+, Safari
xmlHttp=new XMLHttpRequest();
}
catch (e)
{
// Internet Explorer
try
  {
  xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
  }
catch (e)
  {
  xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
}
return xmlHttp;
}
2.交互
function showRSS(str)
{
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
  {
  alert ("Browser does not support HTTP Request")
  return
  }
var url="getrss.php"
url=url+"?q="+str
url=url+"&sid="+Math.random()
xmlHttp.onreadystatechange=stateChanged
xmlHttp.open("GET",url,true)
xmlHttp.send(null)
}
function stateChanged()
{
if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
  {
  document.getElementById("rssOutput")
  .innerHTML=xmlHttp.responseText
  }
}