Gamepad support (SNES) for Scratch 3 using the HTML5 Gamepad API.
Check the keys for your controller here: https://greggman.github.io/html5-gamepad-test/
Read the wiki here (https://github.com/LLK/scratch-gui/wiki/Getting-Started) to get your local copy of Scratch 3.
Then insert the index.js file in this repo to the directory scratch-vm/src/extensions/scratch3_gamepad.
How to edit the menu of the Scratch GUI to make your extension appear in the menu is explained here: https://medium.com/@hiroyuki.osaki/how-to-develop-your-own-block-for-scratch-3-0-1b5892026421