xmlhttp application

1. Xmlhttp is a browser object that can be used to simulate HTTP GET and POST requests. Cooperating with JavaScript, it can realize the regular data update of page data without refreshing . If it is used in chat rooms and text live broadcasts, it can achieve better visual effects.

 

2. XmlHttp is implemented as an ActiveX object in IE, usually using var xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); you can also use var xmlhttp = createobject("MiCROSOFT.XMLHTTP") to create an object, and then use the object The open method to issue an Http request.

 

3. Code example:

var strURL = admin;

function xmlhttpPost(cell,strURL,action) {
	    var xmlHttpReq = false;
	    var self = this;
	    if (window.XMLHttpRequest) {
	        self.xmlHttpReq = new XMLHttpRequest();
	    }
	    else if (window.ActiveXObject) {
	        self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
	    }
	    self.xmlHttpReq.open('POST', strURL, true);//Will enter the corresponding servlet
	    self.xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
	    self.xmlHttpReq.onreadystatechange = function() {
	        if (self.xmlHttpReq.readyState == 4 ) {
	        	if(self.xmlHttpReq.status==200){
		           // updatepage(self.xmlHttpReq.responseText,responsediv);
		           var responseMsg = self.xmlHttpReq.responseText;
		           responseEvent(cell,responseMsg);
	        	}else{
					alert('Ajax Request Error.');
				}
	        }
			
	    }
	    self.xmlHttpReq.send(action);
	}

 

application/x-www-form-urlencoded: key-value pair form submission

 When the action is get, the browser uses the x-www-form-urlencoded encoding method to convert the form data into a string (name1=value1&name2=value2...), and then appends the string to the back of the url, separated by ? , load this new url. When the action is post, the browser encapsulates the form data into the http body and sends it to the server. 

 // The requested status has 5 values: 0=uninitialized; 1=loading; 2=loaded; 3=interactive; 4=completed;
    if (xmlHttpReq.readyState == 4) {
        // 200 corresponds to OK, such as 404 = page not found
        if (xmlHttpReq.status == 200) {
            // alert(xmlHttpReq.responseText);
        }
    }

refer to:
1.http://blog.csdn.net/main_xtgjfge/article/details/18960409