BP Z
Purim there’s a specific mitzvah of simcha, however Chanukah does involve simcha as we say Hallel and part of giving Shvach and Hodaah to Hashem is being Besimcha. The Simcha comes from recognizing how great Hashem is and how much he loves us and just how He saved us then he will save us again in the very near future and bring Moshiach Tzidkeinu. Amen.