Yes.

literally str or it will pr-str / .toString ?

If you use the react dev tools browser plugin I believe it will show you what the key is for a particular component.

Actually, my bad - it's React that does that:

if (hasValidKey(config)) {
      key = '' + config.key;
    }

All that Reagent does is:

(when-some [key (key-from-vec v)]
      (set! (.-key jsprops) key))

pass directly to react. awesome @U2FRKM4TW. thnks