A simple small demo of AJAX based on JavaScript

function prepareForms() {
 for(var j=0 ; j<document.forms.length ; j++){
  var this_forms = document.forms[j];
  resetFields(this_forms);
   this_forms.onsubmit = function () {
    if(!validateForm(this)) return false; //进行浏览器端表单验证
    var article = document.getElementsByTagName("article")[0];
    if(submitFormWithAjax(this,article)) return false; //代表防止重复提交 实际的提交已经完成
   return true;
   }
 }
}

function displayAjaxLoading(element) {
 while(element.hasChildNodes()){
  element.removeChild(element.lastChild); //如果还有子节点 重复删除 直到内部为空
 }
 var content = document.createElement("img");
 content.setAttribute("src","images/loading.gif");
 content.setAttribute("alt","loading....");
 element.appendChild(content);
} //拿到元素 清空内部 并添加一个img
function submitFormWithAjax(whichform,thetarget) {
 var request = getHTTPObject();
 if(!request){return false ;}
 displayAjaxLoading(thetarget);//调用加载方法
 var dataParts = [];
 var element; //提前创建要用的容器
 for(var i=0 ; i<whichform.elements.length ; i++){
  element = whichform.elements[i];
  dataParts[i] = element.name + "=" +encodeURIComponent(element.value) //把元素的名字和值转化成URL编码放入容器中
 }
 var data = dataParts.join("&"); //把数组转化成一串字符串 每个项目之间用&连接
 request.open("post",whichform.getAttribute("action"),true); //向表单目标地址准备提出名为post的请求
 request.setRequestHeader("content-type","application/x-www-form-urlencoded");//设置头部信息
 //获取请求后就会调用一下的 方法 算是一个触发器 服务器会执行以下内容
 request.onreadystatechange = function () {
  if(request.readyState == 4){
   if(request.status == 200 || request.status == 0){
    var matches = request.responseText.match(/<article>([\s\S]+)<\/article>/) //捕获文本
    if(matches.length>0){
     thetarget.innerHTML = matches[1]; //正则表达式返回0为包含<article> 1为不包含的版本
    }
    else {
     thetarget.innerHTML = "<p>sorry not find</p>";
    }
   }
   else {
    thetarget.innerHTML = "<p>" + request.statusText + "</p>";
   }
  }
 }
 request.send(data); //对目标服务器发送请求
 return true;//代表函数执行完毕
}