[brainflake]

Great comment - I do think the whole 'async by default' is a huge benefit, but I would add an asterisk and say you can technically write a module that performs synchronous I/O if you wanted to (see, for example, synchronous filesystem calls). So there's a possibility some random synchronous code blocking could happen with an untrusted module, albeit very unlikely. As far as I know the fs.*FileSync calls are the only ones.