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