A client script is uniquely identified by its key and its type. Scripts with the same key and type are considered duplicates. Only one script with a given type and key pair can be registered with the page. Attempting to register a script that is already registered does not create a duplicate of the script.

Call the erload:System.Web.UI.ClientScriptManager.IsClientScriptBlockRegistered method to determine whether a client script with a given key and type pair is already registered and avoid unnecessarily attempting to add the script.

In this overload of the erload:System.Web.UI.ClientScriptManager.RegisterClientScriptBlock method, you must make sure that the script provided in the script parameter is wrapped in a <script> element block.

The erload:System.Web.UI.ClientScriptManager.RegisterClientScriptBlock method adds a script block to the top of the rendered page. The script blocks are not guaranteed to be output in the order they are registered. If the order of the script blocks is important, use a System.Text.StringBuilder object to gather the scripts together in a single string, and then register them all in a single client script block.