The Tibetan Buddhist tradition also speaks of empathetic joy, but it places even more emphasis on rejoicing in virtue, which is the root of happiness. They say this is a direct antidote for jealousy, inasmuch as jealousy is the inability to bear another person's happiness and success. Note that in the Theravada practice, the first step is focusing on a joyful person other than yourself. In the Tibetan Buddhist practice of rejoicing in the good, it's perfectly appropriate to start with yourself. This is a tremendously rich practice, and it's so simple. There's no notion of achievement, you just do it and it's immediately beneficial.

B. Alan Wallace in The Four Immeasurables: Practices to Open the Heart