To be pedantic, all JavaScript functions block the event loop. It's just that the vast majority of functions execute so quickly that the amount of time your function blocks is very short.

I once had a loop that processed tons of data and would block the event loop for 1-3 seconds. I ended up solving it by writing an asynchronous loop which used promises and process.nextTick() to make each iteration a separate execution block on the event loop. But I've only had to do something weird like that once in 10 years of node development.