Script Lab is a Microsoft garage project which initiated with summer hackathon held back in 2016. Creator main focus is to build a platform where build add-ins simple and with less knowledge curve for web developers. It is simple but it does not mean it is not powerful. Let’s go through below slider where you could kick start on developing Office extended apps.
Get Script Lab
https://aka.ms/getscriptlab – install
Office Add-ins UX design patterns
Office JS API reference