关于JS异步刷新

1.页面上<div id ="iframe" >显示新的请求页面</div>
  页面请求：javaScript:onlink(url);
2.js脚本
function createXMLHttpRequest(){
if(window.ActiveXObject){
  try {
    request = new ActiveXObject("Msxml2.XMLHTTP");
  } catch (othermicrosoft) {
    try {
      request = new ActiveXObject("Microsoft.XMLHTTP");
    } catch (failed) {
      request = false;
    }
   }else{
//其他浏览器
   xmlHttp = new XMLHttpRequest();
  }
}

function onshow(){
if(xmlHttp.readyState==4){
   if(xmlHttp.readyState==200){
    var info = xmlHttp.responseText;
    doucment.getElementById("iframe").innerHTML = info;
   }
}
}

function onLink(url){
createXMLHttpRequest();
xmlHttp.open("post",url,true);
xmlHttp.onreadyStatechage = onshow();
xmlHttp.send(null);
}