How to ensure javascript is included only once when used inside an ASCX

I've an ASCX includes a javascript. If I use this ASCX more than once on a page I have the javascript definition r开发者_JS百科epeated.

Is there a standard clean way to prevent this without define it on a masterpage?

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Check out the ClientScriptManager class. Specifically the RegisterClientScriptBlock and RegisterClientScriptInclude methods.