UXP for Web Developers
It's not sufficient to know those three technologies when writing UXP plugins; as a developer, you also have to be familiar with the host application's API. This is where the Web and UXP seriously diverge. There's nothing like an application API for websites, yet to accomplish anything useful in XD, Photoshop, or any other Creative Cloud application that supports UXP, you have to know the app.
UXP plugins also have a different directory structure than typical websites. There is a required manifest file at the top level of the directory. There is also a set of icons which contains png images that are used when a panel is minimized in Photoshop. While these icons are optional for development, they are mandatory for distribution; your plugin will be fail submission if it lacks the proper icon structure.