I remember what functions exist in many languages, then do a search to find out what that particular language calls them. Most languages have a similar set of basic functions (except those languages that don't support higher-order functions cough), and that set really isn't very big. Most of what ZozoFouchtra lists exist under some alias in all languages that can handle them. For example, I may search for “js fold” (knowing foldl and foldr from Haskell), which takes me directly to MDN's page about Array.prototype.reduce(). I don't use JS much, but when I do, this is my workflow.