Like most Team Fortress 2 players long-sick of Valve's neglect of the game, I jumped over to Overwatch and never looked back. As a Demoman main, Junkrat looks like a perfect fit, right?
Junkrat's kit shares a lot of similarities with Demoman's. While Team Fortress 2 lets you swap out different parts of your loadout, Overwatch heroes' abilities will never change. That being said, Junkrat's abilities have a lot of overlap with vanilla Demoman. Most notably, exploding projectiles that bounce and a sticky mine.
In many ways, Junkrat is an easier version of Demoman. Junkrat's bombs and mine do not damage him, and using the mine to jump is far easier than sticky jumping in TF2.
Junkrat has his trap, which Demoman does not have an answer to. Junkrat also has his RIP-tire ult, which is unique to him as well. Junkrat has no unique melee option.