Random clipping masks script

//@target illustrator

// Main function
function main() {
  var extList = ['jpeg', 'jpg']; // Supported file formats
  var isInclSubfol = true; // Get files from subfolders
  var isToCenter = false; // Align image to mask center
  var filesPath = decodeURIComponent(Folder.desktop + '/images'); // Source folder

  if (!documents.length) {
    return;
  }

  if (!app.selection.length || app.selection.typename === 'TextRange') {
    return;
  }

  var doc = app.activeDocument;
  var docSel = app.selection;
  var length = docSel.length;
  var files = getFolderFiles(Folder(filesPath), extList, isInclSubfol);
  var randomFiles = getRandomElements(files, length);
  var mask, img;

  for (var i = 0; i < length; i++) {
    mask = docSel[i];
    if (mask.typename !== 'PathItem' && mask.typename !== 'CompoundPathItem') continue;

    img = doc.placedItems.add();
    img.file = new File(randomFiles[i]);
    img.name = randomFiles[i].name.replace(/\.[^\.]+$/, '');
    
    img.move(mask, ElementPlacement.PLACEAFTER);

    if (isToCenter) {
      setCenterPosition(img, mask);
    } else {
      setRandomRelativePosition(img, mask);
    }

    img.selected = true;
    mask.selected = true;
    app.executeMenuCommand('makeMask');

    app.selection = [];
  }

  app.redraw();
}

function getFolderFiles(dir, ext, isInclSubfol) {
  var fList = dir.getFiles();
  var regexp = new RegExp(ext.join('|'));
  var arr = [];

  for (var i = 0, len = fList.length; i < len; i++) {
    var f = fList[i];
    if (isInclSubfol && f instanceof Folder) {
      arr = arr.concat(getFolderFiles(f, ext, isInclSubfol));
    } else if (f instanceof File) {
      var name = f.name.toLowerCase();
      // Ignore macOS hidden files
      if (!/^\._|ds_store/i.test(name)
          && regexp.test(/\.[^\.]+$/g.exec(name)[0])) {
        arr.push(f);
      }
    }
  }

  return arr;
}

function getRandomElements(arr, num) {
  var shuffled = arr.slice(0);
  var j, tmp;
  var result = [];

  if (num > arr.length) {
    for (var i = 0; i < num; i++) {
      var index = Math.floor(Math.random() * arr.length);
      result.push(arr[index]);
    }
  } else {
    for (var i = shuffled.length - 1; i > 0; i--) {
      j = Math.floor(Math.random() * (i + 1));
      tmp = shuffled[j];
      shuffled[j] = shuffled[i];
      shuffled[i] = tmp;
    }
  
    result = shuffled.slice(0, num);
  }

  return result;
}

function setCenterPosition(a, b) {
  var top = b.top - ((b.height / 2) - (a.height / 2));
  var left = b.left + (b.width / 2) - (a.width / 2);
  a.top = top;
  a.left = left;
}

function setRandomRelativePosition(a, b) {
  var bndsB = b.geometricBounds;
  var minX = bndsB[0];
  var maxY = bndsB[1];
  var maxX = bndsB[2] - a.width;
  var minY = bndsB[3] + a.height;
  
  a.position = [
    Math.random() * (maxX - minX) + minX,
    Math.random() * (maxY - minY) + minY
  ];
}


// Run script
try {
  main();
} catch (e) {}