Javascript-based browser-compatible Ajax

<Script language = "JavaScript" type = "text/JavaScript">

// Create an XMLHTTPRequest object compatible with the browser

Function createxmlhttp ()
{
VaR XMLHTTP;
If (window. activexobject)
{
VaR arr = ["msxml2.xmlhttp. 6.0", "msxml2.xmlhttp. 5.0 ",
"Msxml2.xmlhttp. 4.0", "msxml2.xmlhttp. 3.0", "msxml2.xmlhttp", "Microsoft. XMLHTTP"];
For (VAR I = 0; I <arr. length; I ++)
{
Try
{
XMLHTTP = new activexobject (ARR [I]);
Return XMLHTTP;
}
Catch (error)
{

}
}
}
Else
{
Try
{
XMLHTTP = new XMLHttpRequest ();
Return XMLHTTP;
}
Catch (othererror)
{

}
}
}
Function xmlpost ()
{
VaR XMLHTTP = createxmlhttp ();
VaR fileurl = 'checkunamehandler. ashx? Uname = '+ username. value; // URL of the accepted value
XMLHTTP. Open ('get', fileurl, true );

XMLHTTP. onreadystatechange = function (){
If (XMLHTTP. readystate = 4 & XMLHTTP. Status = 200)
{
VaR result = XMLHTTP. responsetext;
Alert (result );
If (result = '0 ')
{
Spcheckname. innerhtml = 'user name is available! ';
Document. getelementbyid ('<% = This. btnsub. clientid %>'). Disabled = '';
}
Else if (result = '1 ')
{
Spcheckname. innerhtml = 'user name occupied! ';
Document. getelementbyid ('<% = This. btnsub. clientid %>'). Disabled = 'Disabled ';
}
}
Else
{
Spcheckname. innerhtml = 'the operation is too fast! Data Verification Failed! ';
}
}

XMLHTTP. Send ('');

}

</SCRIPT>

Note:

XMLHTTP. status value (HTTP status table)
0 **: not started
1 **: request received, continue processing
2 **: The operation is successfully received, analyzed, and accepted.
3 **: the request must be further processed.
4 **: The request contains an error syntax or cannot be completed
5 **: the server failed to execute a fully valid request.

100 -- the customer must continue to send the request
101 -- the client requests the server to convert the HTTP protocol version according to the request

200 -- transaction successful
201 -- prompt to know the URL of the new file
202 -- accept and process, but not complete
203 -- the returned information is uncertain or incomplete
204 -- the request is received, but the returned information is null.
205 -- when the server completes the request, the user agent must reset the file that has been browsed.
206 -- the server has completed some users' GET requests

300 -- the requested resources can be obtained in multiple places
301 -- Delete request data
302 -- request data found at other addresses
303 -- we recommend that you access other URLs or access methods.
304 -- the client has executed get, but the file has not changed
305 -- the requested resource must be obtained from the address specified by the server
306 -- used in the previous HTTP VersionCode, Which is not used in the current version
307 -- declaring temporary deletion of requested resources

400 -- incorrect request, such as syntax error
401 -- authorization request failed
402 -- retain valid chargeto header response
403 -- the request is not allowed
404 -- no file, query, or URL found
405 -- the method defined in the request-line field is not allowed.
406 -- the requested resource is inaccessible due to the user's accept drag.
407 -- similar to 401, the user must first be authorized on the Proxy Server
408 -- the client did not complete the request within the specified time
409 -- the request cannot be completed due to the current resource status
410 -- this resource is no longer available on the server and there is no further reference address
411 -- the server rejects the User-Defined Content-Length attribute request
412 -- one or more request header fields are incorrect in the current request
413 -- the requested resource is larger than the size allowed by the server
414 -- the requested resource URL is longer than the length allowed by the server
415 -- the requested resource does not support the format of the requested project
416 -- The request contains the range request header field. There is no range indication value in the current request resource range, and the request does not contain the IF-range request header field.
417 -- the server does not meet the expectation specified in the header field of the response CT request. If it is a proxy server, it may be that the next-level server cannot meet the request

500 -- Internal error occurred on the server
501 -- the server does not support the requested function
502 -- the server is temporarily unavailable, sometimes to prevent system overload
503 -- server overload or service suspension
504 -- the gateway is overloaded. The server uses another gateway or service to respond to the user. The waiting time is long.
505 -- the server does not support or reject the specified HTTP version in the Request Header

1xx: Information Response class, indicating that the request is received and processed continuously
2XX: Successful response class, indicating that the action is successfully received, understood, and accepted
3xx: redirect response class. To complete the specified action, you must accept further processing.
4xx: client error. The client request contains a syntax error or cannot be correctly executed.
5xx: server error. The server cannot correctly execute a correct request.