ASP. NET Ajax client framework not loaded, sys undefined Processing Method

I just saw a post in the Forum saying"ASP. NET Ajax client framework not loaded""Sys" undefined"This error. I think of the processing method when I used the Ajax control package four years ago. Post it for reference.

Principle: in Ajax, sessions are easy to lose. Therefore, when control is returned to the browser, a function is added to scriptmanager, which can be directly used on the page.

SYS. webforms. pagerequestmanager. getinstance (). add_endrequest (endrequesthandler); function endrequesthandler (sender, argS) {If (ARGs. get_error ()! = Undefined) {If (ARGs. get_error (). message. substring (0, 51) = "sys. webforms. pagerequestmanagerparsererrorexception ") {// window. location. reload (); // handle errors when a session is lost. You can define it by yourself. Document. getelementbyid ("Login Control ID"). Click ();} else {alert ("error occurred! The cause may be incomplete data or network latency. "); // Handle other errors. } Args. set_errorhandled (true );}}