Path to Photoshop Plugins/Panels Assets Folder

Question

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

Answer 1

Perfect Tom - works like a charm.
One last question and I hope not to bother you anymore.
This is going back to the last script you helped me with in opening a file from the extension panels folder (everything is working perfectly). I want to add one last item to the script that automatically closes the file from the extension folder without saving. These are template files that I do not want the user changing.
The steps of the script are:
1. Open the file from the extensions folder
2. Duplicate the layer to another open file
3. Close the file - This is where I want the file closed without saving in case the user duplicates the layer in to the same file that came from the extension folder.
I have this code, but do not know how or where to put it:
app.activeDocument.close(SaveOptions.DONOTSAVECHANGES);
/* LSS 1  */
// Open File
function selLssall(inPanelLocation)
  var idOpn = charIDToTypeID( "Opn " );
    var desc176 = new ActionDescriptor();
    var idnull = charIDToTypeID( "null" );
    desc176.putPath( idnull, new File( inPanelLocation + "/lss/lss-1.psd" ) );
  executeAction( idOpn, desc176, DialogModes.NO );
// Duplicate Layer and select the file to insert the layer into
    ErrStrs = {};
ErrStrs.USER_CANCELLED=localize("$$$/ScriptingSupport/Error/UserCancelled=User cancelled the operation");
try {var idDplc = charIDToTypeID( 'Dplc' );    
    var desc1020 = new ActionDescriptor();    
    var idnull = charIDToTypeID( 'null' );        
    var ref834 = new ActionReference();        
    var idLyrsp = charIDToTypeID( 'Lyr ' );        
    var idOrdn = charIDToTypeID( 'Ordn' );        
    var idTrgt = charIDToTypeID( 'Trgt' );        
    ref834.putEnumerated( idLyrsp, idOrdn, idTrgt );    
    desc1020.putReference( idnull, ref834 );
    executeAction( idDplc, desc1020, DialogModes.ALL );
    } catch(e){if (e.toString().indexOf(ErrStrs.USER_CANCELLED)!=-1) {;
            } else{alert(localize("$$$/ScriptingSupport/Error/CommandNotAvailable=The command is currently not available"));}}
// Close File - this is where I want the file close with out saving it
    ErrStrs = {};
ErrStrs.USER_CANCELLED=localize("$$$/ScriptingSupport/Error/UserCancelled=User cancelled the operation");
try {var idClssp = charIDToTypeID( 'Cls ' );
    executeAction( idClssp, undefined, DialogModes.ALL );
    } catch(e){if (e.toString().indexOf(ErrStrs.USER_CANCELLED)!=-1) {;
            } else{alert(localize("$$$/ScriptingSupport/Error/CommandNotAvailable=The command is currently not available"));}}
One again thanks - Sam