Most bands provide a “laptop DJ” service. This isn’t the same as providing the service of a professional DJ who reads the room and adapts to the feel on the night. Instead, they will have a playlist (usually on something like Spotify or iTunes) that they play out of their PA system. It's worth checking the details of this with the band, as some wedding bands only provide the live music and prefer to leave the rest of the evening's music to the couple or a professional DJ.