For me it looks like he's just using Haskell conventions. People in Haskell land use such short variable names for abstract variables. (I.e. when you don't really know much about their type.)
itoa would be familiar to any C programmer (Integer TO Ascii)
I am familiar with atoi but I have never seen itoa, one of the printf family is usually used. However looking it up, a few websites list the function but clearly say that it isn't ANSI C.
Fair enough, but there's a lot of people who know JS, don't write JS like C and just want types.