How to send and receive requests using Ajax

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Basically, Ajax can receive all the information that the browser can receive, ex: string, html tag, css tag, xml format content, json format content and so on.

/ / IE browser if (ActiveXObject) {/ / the latest version of Microsoft AJAX var ajax = new ActiveXObject ("Msxm12.XMLHTTP.6.0");} else {/ / mainstream browser var ajax = new XMLHttpRequest ();} / create HTTP request / / open (method, url, asynchronous, user, password) / / method: request method (post,get) / / url: request address (specific address to receive data) / / asynchronous: synchronous or asynchronous request (true is asynchronous, false is synchronous, default is true, but left empty) / / user: (specify request user name, but leave it empty) / / password: (specify request password, but leave it empty) ajax.open ('get','url') Ajax.onreadystatechange = function () {if ((ajax.readyState==4) & & (ajax.status) = = 200) {alert (ajax.responseText); / / returned data content} else {alert ('request failed');}} / / send request, content is the content to be sent, if not, enter null send (content) / / if you are using post method to request, set the HTTP header ajax.setRequestHeader ("Content-Type", "application/x-www-form-urlencoded") before send;

The onreadystatechange event of ajax receives up to four change states

The returned status value of readystate:

0 (uninitialized) object has been established

1 (initialization) open method has been called

2 (send data) send method has been called

3 (data transfer) some data has been returned

4 (completed) request succeeded

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