ClientScriptManager.IsOnSubmitStatementRegistered Method (String)
Determines whether the OnSubmit statement is registered with the Page object using the specified key.
Assembly: System.Web (in System.Web.dll)
Call this method before calling the RegisterOnSubmitStatement method to avoid registering duplicate OnSubmit statements. This is particularly important if the statement requires a large amount of server resources to create.
A statement is uniquely identified by its key and its type. Statements with the same key and type are considered duplicates.
Available since 2.0