Though Joker’s Justice League role has very little to do with Harley, this is a nice nod to the character’s past. Suicide Squad didn’t factor into Snyder’s grand DCEU plan, but it did exist within the same continuity. Many have noted that, for the most part, Justice League is moving away from Suicide Squad when it comes to the Joker, but the inclusion of Harley’s guns is one way the two movies remain connected. It’s a notable character beat, and one Snyder must’ve thought out carefully.
The Joker has been at the forefront of several pieces of Justice League marketing, though he’ll only really factor into the Knightmare sequence. Most excitingly, he appears to be teaming up with Batman somehow, which is a thrilling story prospect. Joker’s presence in the film just supports how much this is entirely Snyder’s work; he wanted to include the iconic villain, and he has. What’s more, he’s given Joker a fitting and compelling story. It’ll be interesting to see it play out next week.