I am interested in this topic. What is it that needs to be distributed: the compiler, the runtime environment, the attached debugger, the package manager client

I am interested in this topic. What is it that needs to be distributed: the compiler, the runtime environment, the attached debugger, the package manager client, the UI availability, the discoverability, the (relatively) safe execution? JavaScript had a lot of things going for it, but I wonder what was the thing that got distributed that won.