Load Transparency from a layer?

Question

How can I load the transparency from a given layer as a selection via script? In the way as if you cmd-klick on a layer palette icon and have the solid pixels in that layer selected.
There is the Selection.load (from: Channel ), and in the Photoshop menue there is also the option to select the Transparency of the active channel but I can't find anything like that in the object Library.
Thanks for your help, Joerg

Answer 1

You can not use a scripting API reference when working with action manager API. You could add by index, but the action manager index for a layer is not the same as the scripting layer index.
If your workflow allows you could make the layer you want to add active, get the action manager index, add by that index and restore the active layer.
function addLayerTransToSelection( layerIndex ){
     try{
          var desc = new ActionDescriptor();
               var ref = new ActionReference();
               ref.putEnumerated( charIDToTypeID( "Chnl" ), charIDToTypeID( "Chnl" ), charIDToTypeID( "Trsp" ) );
               ref.putEnumerated( charIDToTypeID("Lyr "), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
               ref.putIndex(charIDToTypeID( "Lyr " ), layerIndex );
               //ref.putName( charIDToTypeID( "Lyr " ), layerName );
          desc.putReference( charIDToTypeID( "null" ), ref );
               var ref1 = new ActionReference();
               ref1.putProperty( charIDToTypeID( "Chnl" ), charIDToTypeID( "fsel" ) );
          desc.putReference( charIDToTypeID( "T   " ), ref1 );
          executeAction( charIDToTypeID( "Add " ), desc, DialogModes.NO );
          return true;
     }catch(e){alert(e);}
     return false;
var ref = new ActionReference();
ref.putEnumerated( charIDToTypeID("Lyr "), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") );
var index = executeActionGet(ref).getInteger( stringIDToTypeID( 'itemIndex' ) );
addLayerTransToSelection( index );