问题
What is the application event/processing timeline for an asynchronous request made to a page method on a Web Form? Looking for a canonical answer or resource.
Note: This is a request for information about how ASP.NET AJAX handles incoming requests made to web services exposed to client script as described here in the section named "Calling Static Methods in an ASP.NET Web Page." This is not to be confused with the page life cycle. It should also be mentioned that [WebMethod] and [ScriptMethod] are features of ASP.NET AJAX, and not XML Web Services, as one might infer when reading certain MSDN documentation, examples of which can be found here and here.
来源：https://stackoverflow.com/questions/28350349/what-is-the-request-life-cycle-for-asynchronous-ajax-asp-net-page-method-calls