Creation of XMLHttpRequest object

First, let’s introduce the XMLHttpRequest object. We all know that Ajax is not just a single technology, but a fusion of several technologies. XMLHttpRequest is the core technology in the Ajax technology system. Without XMLHttpRequest, the other Ajax technologies cannot become an organic whole. In Ajax applications, the XMLHttpRequest object is responsible for sending user information to the server asynchronously and receiving response information and data returned by the server.

XMLHttpRequest is an object of the XMLHttp component. Using XMLHttpRequest can partially update web page information without submitting the entire page to the server. Maybe it’s a bit abstract. Everyone often goes to QQ space to see what their friends are doing. Some friends have shared videos. After we click play, the mouse and keyboard do not lose their mobility either during the video buffering or during playback. We can continue browsing. For other dynamics, when we slide the mouse wheel up and down, the video page also moves up and down following the current position we browse, as shown in the figure below. Such a function can be achieved through Ajax.

The XMLHttpRequest object provides a series of properties and methods to send asynchronous HTTP requests to the server. When the server processes user requests, the XMLHttpRequest object reflects the status of the HTTP request in real time through the status value of the attribute and guides JavaScript to perform corresponding processing based on the obtained status. In addition, when the server successfully responds to the user's action and returns the user, the response series methods provided by XMLHttpRequest can assemble the returned data into text format, XML format or unsigned JavaScript script processing provided by byte data format.

Before using the XMLHttpRequest object to send requests and process responses, you must use javascript to create an XMLHttpRequest object. Since the XMLHttpRequest object is not yet a W3C standard, the creation methods are different in new versions of IE browsers, old versions of IE browsers, and non-IE browsers. Therefore, you need to determine the browser type before creating an XMLHttpRequest object. For IE browsers with lower versions, you need to use Microsoft.XMLHTTP, and for IE browsers with higher versions, you need to use Msxml2.XMLHTTP.

The following is the code to create the XMLHttpRequest object:

<span style="font-family:KaiTi_GB2312;font-size:18px;">    <script language="javascript" type="text/javascript">
        var xmlHttp;
        //使用新版本的IE创建XMLHttpRequest对象
        try {
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            //使用旧版本的IE创建XMLHttpRequest对象
            try {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (E) {}
        }
        //使用其他浏览器创建XMLHttpRequest对象
        if (!xmlHttp && typeof XMLHttpRequest !=&#39;undefined&#39;) {
            try{
                xmlHttp=new XMLHttpRequest();
            } catch (e) {
                xmlHttp = false;
            }
        }
    </script></span>

From the code We can see that although logical judgment is required, creating an XMLHttpRequest object is not complicated. My understanding of XMLHttpRequest is not very thorough. I just compiled it based on the examples in the video and the knowledge in the Ajax programming technology textbook. I hope everyone can communicate more and make progress together.

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