Drop Shadow Multi

/*
This script applies a Drop Shadow effect to selected layers in After Effects.
The topmost selected layer acts as a control layer with adjustable Drop Shadow properties.
Other selected layers have Drop Shadow effects linked via expressions to the control layer.
*/

var selectedLayers = app.project.activeItem.selectedLayers;

if (selectedLayers.length > 0) {
  app.beginUndoGroup("Apply Drop Shadow");

  // Convert selectedLayers to array and sort by index ascending (topmost first)
  var layers = [];
  for (var i = 0; i < selectedLayers.length; i++) {
    layers.push(selectedLayers[i]);
  }
  layers.sort(function(a, b) {
    return a.index - b.index;
  });

  var topLayer = layers[0];
  var controlLayerName = topLayer.name;

  // Add Drop Shadow effect to control layer and set properties
  var dropShadow = topLayer.property("Effects").addProperty("Drop Shadow");
  dropShadow.property("Opacity").setValue(40);
  dropShadow.property("Softness").setValue(250);
  dropShadow.property("Direction").setValue(0);
  dropShadow.property("Distance").setValue(0);

  // Add Drop Shadow to other layers and link properties to control layer via expressions
  for (var i = 1; i < layers.length; i++) {
    var layer = layers[i];
    var layerDropShadow = layer.property("Effects").addProperty("Drop Shadow");
    layerDropShadow.property("Opacity").expression = 
      'thisComp.layer("' + controlLayerName + '").effect("Drop Shadow")("Opacity")';
    layerDropShadow.property("Softness").expression = 
      'thisComp.layer("' + controlLayerName + '").effect("Drop Shadow")("Softness")';
    layerDropShadow.property("Direction").expression = 
      'thisComp.layer("' + controlLayerName + '").effect("Drop Shadow")("Direction")';
    layerDropShadow.property("Distance").expression = 
      'thisComp.layer("' + controlLayerName + '").effect("Drop Shadow")("Distance")';
  }

  app.endUndoGroup();
} else {
  alert("No layers selected. Please select at least one layer.");
}