I agree with Jeremy, over emphasize Functional Programming (FP)may be not a good and practically way to find good developers. Knowing popular terms and concepts does not help differentiate a good candidate from a bad one who may just quickly catch up some new things. For me FP is really just doing immutable and stateless with some recursive calls. FP can work with OOP peacefully together.

“Don’t forget, in some languages (including JavaScript), you’ll run into problems when your program makes a large number of recursive calls in a single operation (at the time of writing, “large” is about10,000 calls in Chrome, 50,000 in Firefox and 11,000 in Node.js).”