A little Clojure(Script) solution for a weird little problem.

reverse-vowels.cljs

#!/usr/bin/env planck

(def vowel? #{\A \a \E \e \I \i \O \o \U \u})

(defn reverse-vowels
  "Takes in a string and reverses all the vowels in the string."
  [in]
  (let [idx->letter (zipmap (range) in)
        idx->vowel (filter (fn [[_ letter]] (vowel? letter)) idx->letter)
        [idxes vowels] ((juxt keys vals) idx->vowel)
        ridx->vowel (zipmap (reverse idxes) vowels)]
    (apply
      str
      (reduce (fn [out [idx letter]] (assoc out idx letter))
              (into [] (range (count in)))
              (merge idx->letter ridx->vowel)))))

(println (reverse-vowels "I love burritos"))
;; => o livu berrotIs