Four steps: easily implement ajax to send asynchronous requests, and four steps: ajax

Four steps: easily implement ajax to send asynchronous requests, and four steps: ajax

Ajax sends asynchronous requests for your reference. The details are as follows:

Step 1(Get XMLHttpRequest)

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

1. Get XMLHttpRequest

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

2. Compile a function to create 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 (" Buddy, what browser are you using? "); Throw e ;}}}}

Step 2(Open the connection to the server)

XmlHttp. open (): used to open a connection to the server. It requires three parameters:

Request Method: GET and POST
Request URL: specify server resources, such as/day23_1/AServlet
Whether the request is asynchronous: if it is true, an asynchronous request is sent; otherwise, a synchronous request is sent.

XmlHttp. open ("GET", "/day23_1/AServlet", true); // for Example

Step 3(Send request)

XmlHttp. send (null): If you do not give it, Some browsers may not be able to send it!

Parameter: The request body content! For a GET request, null is required.
For POST requests

XmlHttp. send ("username = zhangSan & password = 123 ");

Step 4:

Register the listener onreadystatechange on an event of the xmlHttp object
The xmlHttp object has five statuses.

0: initialization is not complete. Only the XMLHttpRequest object has 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: The request sending is complete. The send () method has been called.
3: start to read Server Response
4: The server read response ends (usually we only care about the final state !!!)

Get the status of the xmlHttp object

Var state = xmlHttp. readyState; // It may be 0, 1, 2, 3, or 4

Get the server response status code (200: Success 304: status has not changed 404 500: Server Error)

Var status = xmlHttp. status; // For example, 200, 404, 500

Get the server response content

Var content = xmlHttp. responseText; // get the content in the text format of the server response (this is more common) var content = xmlHttp. responseXML; // get the xml response content of the server response. It is a document object!

So the listener should write like this

XmlHttp. onreadystatechange = function () {// this method is called if (xmlHttp. readyState = 4 & xmlHttp. status = 200) {// dual judgment: determines whether the status is 4 and whether it is 200 var text = xmlHttp. responseText ;}};

The above is all the content of this article. I hope it will be helpful for your learning and support for helping customers.