joyfulness       
noun [ U ] uk/ˈdʒɔɪ.fəl.nəs/ us/ˈdʒɔɪ.fəl.nəs/
 欢欣,高兴,喜悦
the quality of being very happy
  The movie's characters are memorable for their robust joyfulness. 这部电影中的人物因其强烈的快乐而令人难忘。 
 Her playing infused the music with a sense of joyfulness. 她的演奏使音乐充满了欢乐。 
 See: joyful
 - More examples
 - In live performances, she radiates a contented joyfulness.
 - The band seemed to lack the joyfulness and spontaneity of their early years.
 - She has a natural joyfulness of character.