In John’s Gospel, judgment does not happen only on the final Judgment Day. It began when Jesus came into the world as the light (3:19; 5:24; 9:39).
Satan is the prince of this world. Satan promotes darkness, leads people into sin, and spreads death. Although Satan’s final defeat is still future, his power was broken through the work of Jesus (see Luke 10:17–18; Mark 3:27).
Now Christ reigns as king in heaven (Acts 7:55–56; Ephesians 1:19–22).