A simple small demo of AJAX based on JavaScript

AJAX

AJAX = Asynchronous JavaScript and XML.

AJAX is not a new programming language, but a new way of using existing standards.

AJAX is the art of exchanging data with a server and updating parts of a web page without reloading the entire page.

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;
   }
 }
}

First call the corresponding verification method and ajax submission method through the form's submission event. If the ajax submission is successful, return false. Intercept the submission event. If ajax fails, submit normally

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
}

Let's see step by step what has been done

The first is to obtain a request object

The second is to call the display method to let the page delete all elements under article And put the load animation

The third request to create a URL encoding uses an array to store an item containing the name and the value escaped by the URL, and then connects each item through & to form a complete string

The fourth is to set the basic attributes of the request, such as naming the target address header file

The fifth is to create a listening program to listen to the request. If successful, fill in the response html into the target article
The sixth official The request is sent successfully and returns true

The above is a simple small demo of JavaScript basic AJAX introduced by the editor. I hope it will be helpful to you. If you have any questions, please leave me a message and the editor will promptly Reply to everyone!

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