Add a custom solid to a selected comp in the project panel

Hi

I cant figure this one out. I really am the phase of learning the wonderfull world of after effect scripting.

I am trying to do a script where i add a custom solid to a selected comp in the project panel. Also do a check to see if a comp is selected.

Here below is my poor attempt.

app.beginUndoGroup("Add solid");

var curItem = app.project.activeItems;

//Check if is a comp is selected

if(curItem == null || !(curItem instanceof CompItem)) {

      alert("Please select a comp");

}else{

alert("You have selected a comp");

curItem.items.addSolid([0.5,0.5,0.5], "My Gray Solid", 1920, 1080, 1.0, 5);

}

app.endUndoGroup();

Please advice...

/HRB