(Sample code by Dave Smart taken from the DroidScript Google Group)

Here is an example of how to list all files on your Lego NXT brick:

//Called when application is started.
function OnStart()
{
	//Create our screen layout.
	CreateLayout();
 
	//Create NXT controller object.
	nxt = app.CreateNxt();   
}
 
//Create the screen layout.
function CreateLayout()
{	
	//Create the layout (with repeating pattern background).
	lay = app.CreateLayout( "Linear", "VCenter,FillXY" );
	lay.SetBackground( "/Sys/Img/Tile.png", "repeat" );
 
	//Create 'Connect' button.
	btn = app.CreateButton( "Connect", 0.3,0.1, "Lego" );
	btn.SetMargins( 0,0,0,0.1 );
	btn.SetOnTouch( btn_OnTouch );  
	lay.AddChild( btn );
	     
	//Create 'List Files' button.
	btnCon = app.CreateButton( "List Files", 0.3, 0.1, "Lego" );    
	btnCon.SetOnTouch( btnCon_OnTouch );     
	lay.AddChild( btnCon ); 
 
	//Add layout to the app.
	app.AddLayout( lay );
}
 
//Called when user presses connect.
function btn_OnTouch()
{        
	//Show list of NXT devices.
	nxt.ShowDevices();
}
 
//Called when 'List Files' button is pressed.
function btnCon_OnTouch( e )
{                           
	alert( ListFiles( "*.*" ) );
}
 
//List files on the NXT using a search pattern.
//eg. "*.rso" finds all sound files.
function ListFiles( pattern )
{   
    app.ShowProgress("Working...");
    
    //Find first matching file on nxt.
    var list = "";
    var inf = nxt.FileFindFirst( pattern );
    if( inf!=null ) list = inf.GetName();    
    
    //Find remaining files.
    while( 1 ) {
	    inf = nxt.FileFindNext( inf.GetHandle() );
	    if( inf==null ) break;
	    list += "," + inf.GetName();	    
    }
    app.HideProgress();
    return list;
}