message: JS: Provides meaningful message in case of compile issues
diff: @@ -103,4 +103,7 @@ if __name__ == "__main__":
  if len(sys.argv) > 2:
  opencvjs = sys.argv[1]
  cvjs = sys.argv[2]
  + if not os.path.isfile(opencvjs):
  + print('opencv.js file not found! Have you compiled the opencv_js module?')
  + exit()
  make_umd(opencvjs, cvjs);
  