Is a story editor window open?

var windows = app.activeDocument.windows,
  nbWindows = windows.length,
  i;
for (i = 0; i < nbWindows; i += 1) {
  if (!windows[i].hasOwnProperty("zoom")) {
    // Let us presume that a window without a zoom method is a story editor window...
    alert("A story editor window is open");
  }
}