Sys.WebForms.PageLoadingEventArgs panelsUpdating Property
Gets an array of HTML <div> elements that represent UpdatePanel controls that will be updated in the DOM as a result of the current asynchronous postback.
To get or set property values for client API properties, you must call property accessor methods that are named with the get_ and set_ prefixes. For example, to get or set a value for a property such as cancel, you call the get_cancel or set_cancel methods.
If the contents of any UpdatePanel controls will be updated as the result of a partial-page update, the panelsUpdating property contains an array that references the corresponding <div> elements. The pageLoading event of the Sys.WebForms.PageRequestManager class uses a PageLoadingEventArgs object to return its event data.