Ajax-onreadystatechange Event (properties of the XMLHttpRequest object)

Three important attributes of the XMLHttpRequest object:

Properties	Description
onReadyStateChange	The function (or function name) is called whenever the ReadyState property is changed.
ReadyState	The state of being xmlhttprequest. Vary from 0 to 4. 0: Request not initialized 1: Server Connection established 2: Request received 3: In Request processing 4: The request is complete and the response is ready
Status	$: "OK" 404: Page Not Found

Example:

1 xmlhttp.onreadystatechange=function () 2   {3  if (xmlhttp.readystate==4 && xmlhttp.status==200)4     {5    document.getElementById ("mydiv"). Innerhtml=xmlhttp.responsetext; 6     }7   }

When ReadyState equals 4 and the status is 200, the response is ready (note: The onReadyStateChange event is triggered 5 times (0-4), corresponding to each change of the readyState. )

Using the Callback function
The callback function is a function that is passed as an argument to another function.

Example:

1 <Scripttype= "Text/javascript">2 varXMLHTTP;3 functionLoadxmldoc (url,cfunc)/ * Pass the parameter, the first parameter represents the URL address, and the second parameter represents the function to execute *  /4 {5 if(window. XMLHttpRequest)6   {//code for ie7+, Firefox, Chrome, Opera, Safari7 XMLHTTP=NewXMLHttpRequest ();8   }9 ElseTen   {//code for IE6, IE5 One XMLHTTP=NewActiveXObject ("Microsoft.XMLHTTP"); A   } - Xmlhttp.onreadystatechange=Cfunc; / * Call function *  / - Xmlhttp.open ("GET", URLs,true); the xmlhttp.send (); - } - functionmyFunction () - { + Loadxmldoc ("/ajax/test1.txt",function() -   { +   if(Xmlhttp.readystate==4 &&Xmlhttp.status== $) A     { at document.getElementById ("mydiv"). InnerHTML=Xmlhttp.responsetext; -     } -   }); - } - </Script>

Ajax-onreadystatechange Event (properties of the XMLHttpRequest object)