I am writing this for making a inquiry.

I need to use a hardware kit with a extension library of Scratch 2.0.

http://llk.github.io/scratch-extension-docs/#serial-device-support

I’m going to make a block to add an Extension to Scratch with javascript as this document.

But, there is no ‘new from file.’ in the picture.

Please, let me know how to solve this problem.