Sympathetic joy is one of the "Four Divine Abodes" - sometimes referred to as the "Four Sublime States":
One of the hardest things for many of us to do is to feel happy when something good happens to another person. Judgment and envy, the tendency to compare and demean, and greed and prejudice narrow our world and make sympathetic joy nearly impossible to experience. But learning to feel joy for others can help transform our own suffering and self-centeredness into joy.
-- Joan Halifax