code: function get_or_create() {
                  if (locked) {
                      setTimeout(wait, 100);
                  } else {
                      locked = true;
  
                      if (phantom_instance != null) {
                          locked = false;
                          resolve(phantom_instance);
                      } else {
                          phantom.create().then((instance) => {
                              phantom_instance = instance;
                              locked = false;
                              resolve(instance);
                          });
                      }
                  }
              }
docs: Creates an instance of PhantomJS if there are no instance created. and returns it. Otherwise, returns the existing instance.