R is not a compiled programing language so you might be looking for the wrong key word. R is an interpreted language so R code gets executed by an R interpreter.
You haven't told us what is your specific use case but if you are looking for an online R session where you can use R interactively, you can use RStudio Cloud.
If you are looking for a working online R console that you can embed into a website for example, I know it is technically possible (Data Camp does it) but I'm not aware of a service that implements it for you.