Script for counting layers in PSD file.

count-layers-psd.js

var totalProgress = 0 // I assume this is defined eleswhere but is needed for the scriptler
function layerCounter(inObj) { // recursive function to count layers
  totalProgress += inObj.artLayers.length;
  for (var i = 0; i < inObj.layerSets.length; i++) {
    totalProgress++;
    layerCounter(inObj.layerSets[i]); // recursive call to layerCounter
  }
  return totalProgress;
}

function getLayerCount() {
  function getNumberLayers() {
    var ref = new ActionReference();
    ref.putProperty(charIDToTypeID('Prpr'), charIDToTypeID('NmbL'))
    ref.putEnumerated(charIDToTypeID('Dcmn'), charIDToTypeID('Ordn'), charIDToTypeID('Trgt'));
    return executeActionGet(ref)
      .getInteger(charIDToTypeID('NmbL'));
  }

  function getLayerType(idx) {
    var ref = new ActionReference();
    ref.putProperty(charIDToTypeID('Prpr'), stringIDToTypeID('layerSection'));
    ref.putIndex(charIDToTypeID('Lyr '), idx);
    return typeIDToStringID(executeActionGet(ref)
      .getEnumerationValue(stringIDToTypeID('layerSection')));
  };
  var cnt = getNumberLayers();
  var res = cnt;
  if (activeDocument.layers[activeDocument.layers.length - 1].isBackgroundLayer) {
    var i = 0;
    res++; // comment out this to exclude background from count
  } else {
    var i = 1;
  };
  for (i; i < cnt; i++) {
    var temp = getLayerType(i);
    if (temp === 'layerSectionEnd') res--;
    // if (temp === 'layerSectionStart') res--; // uncomment to count just artLayers
  };
  return res;
};

function main() {
  var answer = confirm('Go through your file and count all the layers?');
  if (answer) {
    var reporter1 = layerCounter(app.activeDocument);
    alert('All done!\nLayer count = ' + reporter1 + ';\nAuthor: github.com/drugoi');
  } else {
    reporter2 = getLayerCount();
    alert('All done!\nLayer count = ' + reporter2 + ';\nAuthor: github.com/drugoi');
  }
}

main();

How to use:

1. Save this .js file to your computer.
2. Open .psd file then: File > Scripts > Browse… and choose count-layers-psd.js