SoFunction
Updated on 2025-04-06

Understanding of xmlHttp object methods and properties

1  The client can passxmlHttpObject (.3.0) sends requests to the http server and uses the document object model(DOM)Process the response.

1.1 My understanding:

  1. Every time a user operates, data will be generated.
  2. passDOMorJSWrite to encapsulate the data, or the browser itselfhttpSome data from the protocol is encapsulated.
  3. passxmlHttpSome methods of the object, passing in data parameters,httpThe server sends a request.
  4. Return result passedDOMPerform processing.

2  xmlHttpMember of the object.

2.1 property

  1. onreadystatechange:whenreadyStateThe event processing handle triggered when the property value changes.

example: = functionHandler;

   function functionHandler() {

if( == 4) {

alert("whenreadyStateStatus is4When this window pops up! ! !");

}

  }

//The handle has only method name, no this pair()”Branch. Pay attention to understanding when assigning values.

  1. readyState:This attribute represents a state; there are five states in total:

0 (not initialized)

The object has been established, but has not been initialized (the open method has not been called yet)

1 (Initialization)

The object has been created and the send method has not been called yet

2 (Send data)

The send method has been called, but the current status and http header are unknown

3 (Data transmission)

Some data has been received, because the response and http headers are incomplete, an error will occur when a responseBody and responseText is obtained.

4 (Complete)

After the data is received, you can obtain the complete response data through responseBody and responseText.

// becausexmlHttpThe writing method is fixed, so each step will be accompanied by a change in state, so the event processing handle is always listened to and the corresponding logic is executed.

Code execution order:

var  xmlHttpReq = new ActiveXObject(".3.0");

("GET", "http://localhost/", false);

();

alert();

 

2.2 method

  1. open(Method, Url, Syn, User, Password);

Create a newxmlHttpWhen an object is created, it is actuallyhttpask.

This method specifies the requested method(GET/POST/PUT/PROPFIND)、 URL,asynchronous(The default istrue), verification information.

Adopt asynchronous(true)When the state changes, it will be calledThe callback function specified by the onreadystatechange property.

  1. send();

The synchronous or asynchronous way of this method depends on the open methodSyn parameter, ifSyn == false, this method will wait for the request to complete or timeout before returning, ifSyn == true, this method will return immediately.