JS encapsulates the same domain, jsonp cross-domain (with code)

This time I will bring you JS encapsulation in the same domain, jsonp cross-domain (with code), JS encapsulation in the same domain, jsonp cross-domain What are the precautions , the following is a practical case, let's take a look one time.

Use native Js to encapsulate an Ajax plug-in, introduce general projects, and transfer data. It feels feasible. . . Let me briefly talk about the ideas. If there are any mistakes, please correct me^_^

1. Ajax core, creating XHR objects

The core of Ajax technology is XMLHttpRequest Object (referred to as , MSXML2.XMLHttp.3.0 and MSXML2.XMLHttp.6.0. Therefore, when creating an XHR object, you must use compatibility writing:

createXHR:function(){
 if(typeof XMLHttpRequest!='undefined'){
 return new XMLHttpRequest();
 }else if(typeof ActiveXObject!='undefined'){
 if(typeof arguments.callee.activeXString!='string'){
 var versions=["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"],i,len;
 for(i=0,len=versions.length;i
 2. The main method attributes of XHR
Method: 
open() method : Accepts 3 parameters, the type of request to be sent, the URL of the request, and the Boolean value of whether to send asynchronously 
send() method: The data to be sent as the request body, if there is no need to send data through the request body , you must pass in null
abort() method: called to cancel the asynchronous request before receiving the response. 
Properties: 
responseText: The text returned as the response body. 
status: HTTP status of the response 
statusText: HTTP status description 
readyState: Indicates the current active stage of the request/response process 
The values ​​are respectively :
0: Not initialized. The open() method has not been called
1: Start. The open() method has been called, but the send() method has not been called
2: Send. The send() method has been called, but no response has been received. 
3: Receive. Partial response data has been received 
4: Complete. All response data has been received and can be used  on the  client. 
onreadystatechangeEvent handling in this exampleFunction: 
var complete=function(){
 if(xhr.readyState==4){
 if((xhr.status>=200&&xhr.status<300)||xhr.status==304){
 if(params.success){
  params.success(xhr.responseText);//执行调用ajax时指定的success函数
  }
 }else{
 if(params.fail){
 params.fail();//执行调用ajax时指定的fail函数
 }else{
 throw new Error("Request was unsucessful:"+xhr.status);
 }
 }
 }
}
Note: The onreadystatechange event handling function must be specified before calling the open() method to ensure cross-browser compatibility . 
3. Sending requests in the same domain
①GET request
The most common request type, often used to query certain information. Information is sent to the server by appending the query's string parameters to the end of the URL. One thing to note with get method requests is that each parameter name and value in the query string must be encoded using encodeURIComponent(), and all name-value pairs must be separated by an ampersand. 
Request method: 
if((this.config.type=="GET")||(this.config.type=="get")){
 for(var item in this.config.data){
 this.config.url=addURLParam(this.config.url,item,this.config.data[item]);//使用encodeURIComponent()进行编码
 }
 xhr.onreadystatechange=complete;
 xhr.open(this.config.type,this.config.url,this.config.async);
 xhr.send(null);
}
②POST request
 is usually used to send data that should be saved to the server. The POST request should submit the data as the body of the request. This will simulate a form submission. That is, set the Content-Type header information to application/x-www-form-urlencoded; charset=UTF-8. 
Serialization function: 
 function serialize(data){
 var val="";
 var str="";
 for(var item in data){
  str=item+"="+data[item];
  val+=str+'&';
 }
 return val.slice(0,val.length-1);
 }
Request method: 
if(this.config.type=="POST"||this.config.type=="post"){
 xhr.addEventListener('readystatechange',complete);
 xhr.open(this.config.type,this.config.url,this.config.async);
 if(params.contentType){
  this.config.contentType=params.contentType;
  }
 xhr.setRequestHeader("Content-Type",this.config.contentType);
 xhr.send(serialize(this.config.data));
}
Some differences between the two requests: 
 ①GET request writes parameter data to the URL, It can be seen in the URL, but not in POST, so GET is not safe and POST is safer. 
②The amount of data transmitted by GET is small and cannot be larger than 2kb. The amount of data transmitted by POST is relatively large and is generally unrestricted by default. 
③The GET server side uses Request.QueryString to obtain the value of the variable, and the POST server side uses Request.From to obtain it. 
④GET adds data to the URL to pass to the server, usually using a? , each data parameter in the following parameters appears in the form of "name=value", and the parameters are distinguished by a connector &. POST data is placed in the HTTP body, and it is organized in more than one way, including & links and delimiters. You can hide parameters and transfer large amounts of data, which is more convenient. 
4. JSONP sends cross-domain requests
 First of all, what is the situation of cross-domain? 
Composition of a domain name: 
http:// www . abc.com: 8080 / scripts/AjaxPlugin.js
协议       子域名      主域名      端口号     请求资源地址
~当协议、子域名、主域名、端口号中任意一个不相同时，都算作不同于。
~不同域之间互相请求资源，就算作“跨域”。
所有的浏览器都遵守同源策略，这个策略能够保证一个源的动态脚本不能读取或操作其他源的http响应和cookie，这就使浏览器隔离了来自不同源的内容，防止它们互相操作。所谓同源是指协议、域名和端口都一致的情况。浏览器会阻止ajax请求非同源的内容。
JSONP(JSON with Padding) 是一种跨域请求方式。主要原理是利用了script 标签可以跨域请求的特点，由其 src 属性发送请求到服务器，服务器返回 JS 代码，网页端接受响应，然后就直接执行了，这和通过 script 标签引用外部文件的原理是一样的。但是jsonp跨域只支持get请求。
JSONP由两部分组成：回调函数和数据，回调函数一般是由网页端控制，作为参数发往服务器端，服务器端把该函数和数据拼成字符串返回。
jsonp跨域主要需要考虑三个问题：
1、因为 script 标签的 src 属性只在第一次设置的时候起作用，导致 script 标签没法重用，所以每次完成操作之后要移除；
2、JSONP这种请求方式中，参数依旧需要编码；
3、如果不设置超时，就无法得知此次请求是成功还是失败；
由于代码有点长，就放个计时器的代码吧，完整代码见AjaxPlugin
//超时处理
if(params.time){
 scriptTag.timer=setTimeout(function(){
 head.removeChild(scriptTag);
 params.fail&¶ms.fail({message:"over time"});
 window[cbName]=null;
 },params.time);
}
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