I want to copy and paste multiple objects from one layer, to multiple other layers at once

if (app.documents.length === 0) {
  alert("No document is open.");
} else {
  var doc = app.activeDocument;
  
  if (doc.selection.length === 0) {
    alert("No items are selected.");
  } else {
    var selectedItems = doc.selection;
    
    // Specify target layer names
    var targetLayerNames = ["Layer 1", "Layer 2", "Layer 3"];
    var targetLayers = [];
    
    for (var i = 0; i < targetLayerNames.length; i++) {
      var targetLayerName = targetLayerNames[i];
      var layer = doc.layers.item(targetLayerName);
      
      if (layer.isValid) {
        targetLayers.push(layer);
      }
    }
    

    if (targetLayers.length === 0) {
      alert("No target layers found.");
    } else {
      for (var j = 0; j < selectedItems.length; j++) {
        var currentItem = selectedItems[j];
        
        for (var k = 0; k < targetLayers.length; k++) {
          var targetLayer = targetLayers[k];
          var newItem = currentItem.duplicate(targetLayer);
        }
      }
      
      alert("Items copied to target layers successfully.");
    }
  }
}

Hi @Eugene Tyson, I have written a script for this too, before I saw yours. Our scripts are basically the same, but I'll post mine here, too, because it does have a couple of differences:

1. I found that I needed to sort the selected items by index so that the order was correct when duplicated (without this, when I select the items one-by-one in different orders I get differently-ordered duplicates).
2. Also I added a UI (optional) for choosing which layers you want to target.

- Mark

/**
 * Duplicate selected items to multiple layers.
 * @author m1b
 * @discussion https://community.adobe.com/t5/indesign-discussions/i-want-to-copy-and-paste-multiple-objects-from-one-layer-to-multiple-other-layers-at-once/m-p/13851545
 */
function main() {

    if (app.documents.length == 0) {
        alert('Please make a selection and try again.');
        return;
    }

    var doc = app.activeDocument;

    var settings = {
        doc: doc,
        showUI: true,
        layers: [
            // just examples, if not showing UI
            doc.layers.itemByName('Layer 2'),
            doc.layers.itemByName('Layer 3'),
        ],
    };

    items = settings.doc.selection;

    if (
        items == undefined
        || items.length == 0
    ) {
        alert('Please make a selection and try again.');
        return;
    }

    // show UI
    if (
        settings.showUI
        && chooseLayers(settings) == false
    )
        // user cancelled UI
        return;

    // sort items by index
    items.sort(function (a, b) { return b.index - a.index });

    // do the duplicating
    for (var i = 0; i < settings.layers.length; i++)
        for (var j = 0; j < items.length; j++)
            items[j].duplicate(settings.layers[i]);

    alert('Duplicated ' + items.length + ' items each to ' + settings.layers.length + ' layers.');

};

app.doScript(main, ScriptLanguage.JAVASCRIPT, undefined, UndoModes.ENTIRE_SCRIPT, 'Duplicate To Layers');


/**
 * Shows UI for selecting layers of document.
 * @author m1b
 * @version 2023-06-09
 * @param {Object} settings
 * @param {Document} settings.doc - an Indesign Document.
 */
function chooseLayers(settings) {

    var allLayers = settings.doc.layers,
        selectedLayerNames = [],
        w = new Window("dialog { text:'Namr', properties:{ resizeable:true } }"),
        layersListBox = w.add("ListBox {alignment:['fill','fill'], properties:{multiselect:true, showHeaders:true, numberOfColumns:1, columnTitles:['Layer'] } }"),
        buttons = w.add("Group { orientation: 'row', alignment: ['right','bottom'], margins:[0,12,0,22] }"),
        cancelButton = buttons.add("Button { text:'Cancel', properties: { name:'cancel' } }"),
        okButton = buttons.add("Button { text:'Rename', properties: { name:'ok' } }");

    // populate layers menu
    for (var i = 0; i < allLayers.length; i++)
        layersListBox.add('item', allLayers[i].name);

    /**
     * Updates `selectedLayerNames`
     * when listbox selection changes.
     */
    layersListBox.onChange = function () {

        var sel = this.selection;
        selectedLayerNames = [];
        settings.layers = [];

        if (sel == null)
            return;

        for (var i = 0; i < sel.length; i++)
            selectedLayerNames.push(sel[i].text);

    };

    if (w.show() == 2)
        // user cancelled
        return false;

    // add the selected layers to settings object
    for (var i = 0; i < selectedLayerNames.length; i++)
        settings.layers.push(settings.doc.layers.itemByName(selectedLayerNames[i]));

};