Implement ajax method to send asynchronous requests-JS Tutorial-php.cn

Implement ajax method to send asynchronous requests

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Release： 2018-04-16 13:45:56

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This time I will bring you the implementation of ajax sending asynchronous request method , what are the precautions for implementing ajax sending asynchronous request, the following is a practical case, let's take a look.

ajax sends an asynchronous request for your reference. The specific content is as follows

First step(Get XMLHttpRequest)

Ajax actually only needs to learn one object: XMLHttpRequest. If you master it, you have mastered ajax!!!

1. Get XMLHttpRequest

Most browsers support:var xmlHttp=new XMLHttpRequest();
IE6.0:var xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
IE5.0 and earlier versions of IE:var xmlHttp =new ActiveXObject("Microsoft.XMLHTTP");

2. Write a function that creates an XMLHttpRequest object

function createXMLHttpRequest(){
     try{
     return new XMLHttpRequest();
     } catch(e){
     try{
     return new ActiveXObject(“Msxml2.XMLHTTP”);
    }catch(e){
     try{
      return new ActiveXObject(“Microsoft.XMLHTTP”);
     }catch(e){
       alert(“哥们儿,你用的是什么浏览器啊?”);
       throw e;
    }
    }
     } 
}

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Step 2(Open the connection to the server)

xmlHttp.open(): used to open a connection with the server, it requires three parameters:

Request method: can be GET or POST
Requested URL: Specify the server-side resource, for example:/day23_1/AServlet
Whether the request is asynchronous: If true, it means sending an asynchronous request, otherwise it is synchronous ask

xmlHttp.open("GET","/day23_1/AServlet",true); //For example

Step Three(Send Request)

xmlHttp.send(null): If not given, some browsers may not be able to send!

Parameter: It is the request body content! If it is a GET request, null must be given.
If it is a POST request, as follows

xmlHttp.send(“username=zhangSan&password=123”);

the fourth step:

0: Initialization is not completed, the XMLHttpRequest object has only been created, and the open() method has not been called.
1: The request has started, the open() method has been called, but the send() method has not been called.
2: Request Sending completion status, the send() method has been called
3: Start reading the server response
4: End of reading the server response (usually we only care about the last status!!!)

Get the status of xmlHttp object

var state = xmlHttp.readyState;//可能是0、1、2、3、4

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Get the status code of the server response (200: Success, 304: Status has not changed, 404 500: Server error)

var status=xmlHttp.status;//例如200、404、500

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Get the content of the server response

var content=xmlHttp.responseText;//得到服务器的响应的文本格式的内容(这更通用)
var content=xmlHttp.responseXML;//得到服务器的响应的xml响应的内容,它是document对象了!

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So the listener should be written like this

xmlHttp.onreadystatechange = function(){
  //xmlHttp的5种状态都会调用本方法
    if(xmlHttp.readyState ==4 && xmlHttp.status == 200){
  //双重判断:判断是否为4状态,而且还要判断是否为200
      var text=xmlHttp.responseText;
     } 
};

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I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the PHP Chinese website!