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