Then, if you use the 'move' method for the flight of the dart, you should come close to where the mouse was when the dart was fired. That is, provided that it moves at a fair rate of speed (the faster, the more accurate).
Put a check in the Dart class, first determine its distance from where the mouse was clicked and set its location there if within one move of the location. If not that close, do the normal move (use an 'if-else').