Make sure to not overlook including "Sys.WebForms.PageRequestManager" in your code when dealing with the undefined condition.
if (typeof(Sys) !== 'undefined') {
Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(function (sender, args) {
{{scopeName}}_init();
});
}
Ensure that the init function is only executed when the document is fully loaded for postback - synchronous section.
When working with ajax requests in a ScriptManager block, remember to register the init function on "add_pageLoaded" for smooth operation on subsequent requests - asynchronous section.
An important step that is often overlooked is also registering "add_endRequest", which helps resolve any issues.
Here is an example of the complete code:
$(document).ready(function () {
// sync
console.log("sync");
{{scopeName}}_init();
// async
pageRequestManager = Sys.WebForms.PageRequestManager.getInstance();
pageRequestManager.add_endRequest({{scopeName}}_onAsyncEndRequest);
pageRequestManager.add_pageLoaded({{scopeName}}_onAsyncPageLoaded});
});
function {{scopeName}}_onAsyncEndRequest(sender, args) {
console.log("async end");
console.log(args);
}
function {{scopeName}}_onAsyncPageLoaded(sender, args) {
console.log("async start");
{{scopeName}}_init();
}