View Ajax from readystate status

Details about five states of readystate

InPragmatic Ajax a Web 2.0 PrimerThe introduction to readystae status is displayed by chance. I feel that this introduction is very practical. The excerpt is as follows:

0: (uninitialized) The send () method has not yet been invoked.
1: (loading) The send () method has been invoked, request in progress.
2: (loaded) The send () method has completed, entire response received ed.
3: (interactive) The response is being parsed.
4: (completed) the response has been parsed, is ready for harvesting.

0-(not initialized) The send () method has not been called
1-(load) The send () method has been called and a request is being sent.
2-(Loading completed) The send () method is executed completely and all response content has been received
3-(interaction) parse the response content
4-(complete) The response content has been parsed and can be called on the client

The five States of readystate are mostly unknown in other books. Like foundations of Ajax, the state "name" -- the state of the request is simply listed in Table 2-2 of the book. the five possible values are 0 = uninitialized, 1 = loading, 2 = loaded, 3 = interactive, and 4 = complete. Ajax in action does not seem to mention the details of these five States at all.

Professional AjaxAlthough not satisfactory, there are still merits:

There are five possible values for readystate:
0 (uninitialized): the object has been created but the open () method hasn' t been called.
1 (loading): the open () method has been called but the request hasn' t been sent.
2 (loaded): The request has been sent.
3 (interactive). A partial response has been already ed.
4 (complete): All data has been encrypted Ed and the connection has been closed.

Readystate has five possible values:
0 (not initialized): (XMLHttpRequest) the object has been created, but the open () method has not been called.
1 (load): the open () method has been called, but no request has been sent.
2 (Loading completed): The request has been sent completely.
3 (interaction): Some response data can be received.
4 (complete): All data has been received and the connection has been closed.

InUnderstanding Ajax: using JavaScript to create rich Internet applicationsIs described in the following table:

Readystate status code
Status of the XMLHTTPRequest object

(0) uninitialized is not initialized
The object has been created but not initialized. (The open method has not been called .)
(XMLHttpRequest) the object has been created, but has not been initialized (the open method has not been called ).

(1) Loading
The object has been created, but the send method has not been called.
(XMLHttpRequest) the object has been created, but the send method has not been called.

(2) loaded
The send method has been called, but the status and headers are not yet available.
The send method has been called, and the (HTTP Response) status and header are not available yet.

(3) Interactive
Some data has been received. Calling the responsebody and responsetext properties at this state to obtain partial results will return an error, because status and Response Headers are not fully available.
Some data has been received. However, if you call the responsebody and responsetext attributes to obtain some results at this time, an error will occur because the status and response header are not fully available.

(4) completed
All the data has been encoded ed, and the complete data is available in the responsebody and responsetext properties.
All data has been received, and the complete data can be extracted from the responsebody and responsetext attributes.

Based on the introduction of the five States of readystate in the above books, I think pragmatic Ajax a Web 2.0 primer is in place because it mentions the issue of parsing the received data, this is not mentioned in other books, and it is the "(3) interaction" stage as a necessary conversion process that exists in "(2) Loading completed" to "(4) the reason between completion is what the task is. To sum up, I think the ideal interpretation method should be to define the States accurately in the "State: task (target) + process + performance (or feature)" expression mode, it is easy to understand.

The following is a summary:

Readystate status description
 
(0) not initialized
In this phase, check whether the XMLHTTPRequest object is created and make preparations for calling the open () method for initialization. If the value is 0, the object already exists. Otherwise, the browser reports an error -- the object does not exist.
 
(1) Load
In this phase, the XMLHTTPRequest object is initialized, that is, the open () method is called, and the object state is set according to the parameter (method, URL, true. And call the send () method to start sending requests to the server. If the value is 1, a request is being sent to the server.
 
(2) Load completed
In this phase, the server receives response data. However, the raw data returned by the server cannot be directly used on the client. If the value is 2, all response data has been received. Prepare for data parsing in the next stage.
 
(3) Interaction
This phase parses the received server response data. That is, the data is converted into a format that can be accessed through the responsebody, responsetext, or responsexml Attribute Based on the MIME type returned by the response header of the server, so as to prepare for the client call. Status 3 indicates that the data is being parsed.
 
(4) Completed
At this stage, it is confirmed that all data has been resolved to the available format of the client, and the resolution has been completed. If the value is 4, the data is parsed. You can use the corresponding attributes of the XMLHTTPRequest object to obtain the data.
 
Specifically, the lifecycle of the XMLHTTPRequest object should include the following stages:

Create-initialize request-Send request-receive data-parse data-complete

In specific applications, the meaning of the five States of readystate (each stage of the lifecycle of the XMLHTTPRequest object) can be clarified to eliminate the mystery of the Ajax core, create a mysterious sense, or be "stunned by others"), quickly grasp the essence, is extremely beneficial to reduce the frustration in learning and enhance self-confidence.

For example, the following example is used:

// Declare an array
VaR States = ["Initializing ...... ",
"Initializing request ...... Successful! <Br/> sending request ...... ",
"Successful! <Br/> receiving data ...... ",
"Done! <Br/> parsing data ...... ",
"Done! <Br/> "];

//Internal callback functionCodeFragment
If(XMLHTTP. readystate=4)
{
VaRSpan=Document. createelement ("span ");
Span. innerhtml=States [XMLHTTP. readystate];
Document. Body. appendchild (SPAN );

If (XMLHTTP. Status =   200 )
{
VaR Xmldoc = XMLHTTP. responsexml;
// Other code
}
// Do not forget to destroy it to prevent memory leakage
XMLHTTP =   Null ;
}
Else
{
VaR Span = Document. createelement ("span ");
Span. innerhtml = States [XMLHTTP. readystate];
Document. Body. appendchild (SPAN );
}

The result is as follows:

Initializing request ...... Successful!
Sending request ...... Successful!
Receiving data ...... Done!
Parsing data ...... Done!

It is easy to understand what the XMLHTTPRequest object is doing at each stage. Therefore, it is easy to have a simple and clear understanding of the core part of Ajax.

Appendix:

Example 1

ReadystateReturns the current status of the XMLHTTP request.
SyntaxLvalue = oxmlhttprequest. readystate;

VaR XMLHTTP;
XMLHTTP =   New Activexobject ( " Msxml2.xmlhttp. 3.0 " );

function send () {
XMLHTTP. onreadystatechange = dohttpreadystatechange;
XMLHTTP. open ( " Get " , " http: // localhost/sample. XML " , true );
XMLHTTP. send ();
}

FunctionDohttpreadystatechange (){
If(XMLHTTP. readystate= 4){
Alert ("Done");
}
}

RemarksVariable. This attribute is read-only and the status is represented by an integer with a length of 4. The definition is as follows:

0 (not initialized) the object has been created, but has not been initialized (the open method has not been called)
1 (initialization) the object has been created and the send method has not been called
2 (send data) The send method has been called, but the current status and HTTP header are unknown.
3 (in data transmission) Some data has been received. Because the response and HTTP headers are incomplete, an error occurs when retrieving part of data through responsebody and responsetext,
4. After receiving the data, you can use responsebody and responsetext to obtain the complete response data.

Example 2

The following example shows how to use VBscript code to read the readystate attribute of the RDS. datacontrol object at runtime. Readystate is read-only.

To test this example, cut the code and paste it to the <body> </body> mark of the standard HTML document, and name it "adcapi9.asp ", the ASP script identifies the server.

< Center >
< H2 > Rds api code examples </ H2 >
< HR >
< H3 > RDS. datacontrol readystate Property </ H3 >
</ Center >
< ! -- RDS. datacontrol -->
< Object Classid = " CLSID: BD96C556-65A3-11D0-983A-00C04FC29E33 "
ID = ADC >
< Param name = " SQL " Value = " Select * from employee for browse " >
< Param name = " Server " Value = " Http: // <% = request. servervariables ( " SERVER_NAME " ) %> " >
< Param name = " Connect " Value = " DSN = adcdemo; uid = adcdemo; Pwd = adcdemo; " >  
< Param name = " Executeoptions " Value = " Adcexecasync " >  
< Param name = " Fetchoptions " Value = " Adcfetchasync " >
</ Object >
< Script Language = " VBScript " >
Sub Window_onload
Select   Case Adc1.readystate
Case   2 : Msgbox   " Executing Query "
Case   3 : Msgbox   " Fetching records in background "
Case   4 : Msgbox   " All records fetched "
End   Select
End sub
</ Script >

 
Refer:
Online manual-51windows. net
ASP technical tutorial