Path to Photoshop Plugins/Panels Assets Folder

I am one of those who is scrambling to recreate a panel that was made in Configurator to HTML5 so please bear with me.

For a javascript I am trying to find the path to a file in the "assets" folder within my panel for both Mac & Windows. I want the path to open a specific file. Here is the base code:

function selLss1(){var idOpn = charIDToTypeID( "Opn " );

    var desc176 = new ActionDescriptor();

    var idnull = charIDToTypeID( "null" );

    desc176.putPath( idnull, new File( "/assets/file.psd" ) );

executeAction( idOpn, desc176, DialogModes.NO );

}

"/assets/file.psd" is the file and I need to know how to tell Photoshop how to find and open this file in Mac's and Windows.

Thanks in Advance - Sam