# [Jelly][1], <s>13 12</s> 11 [bytes][2]

-1 byte thanks to @Luis Mendo (use `Ḃ` to replace `%2`)  
-1 byte thanks to @Dennis (use a string compression)

    Œlf“¡ẎṢɱ»LḂ

All test cases are at **[TryItOnline][3]**

How?

    Œlf“¡ẎṢɱ»LḂ - Main link takes an argument - s
    Œl          - lowercase(s)
       “¡ẎṢɱ»   - string of lowercase vowels (compression using the words a and eoui)
      f         - filter - keep only the vowels
             L  - length - the number of vowels
              Ḃ - Bit (modulo 2)
      
---
**Non-competing, 5 bytes** (since I just added the function `Øc`)

    fØcLḂ

Test cases also at **[TryItOnline][4]**

Same as above, but `Øc` yields the Latin alphabet's vowels, `'AEIOUaeiou'`


  [1]: https://github.com/DennisMitchell/jelly
  [2]: https://github.com/DennisMitchell/jelly/wiki/Code-page
  [3]: http://jelly.tryitonline.net/#code=xZJsZuKAnMKh4bqO4bmiybHCu0zhuIIKxbzDh-KCrEvigqxZ&input=&args=InRyZWVzIiwiYnJ1c2giLCJDQXRzIiwiU2F2b2llIiwicmh5dGhtIg
  [4]: http://jelly.tryitonline.net/#code=ZsOYY0zhuIIKxbzDh-KCrEvigqxZ&input=&args=InRyZWVzIiwiYnJ1c2giLCJDQXRzIiwiU2F2b2llIiwicmh5dGhtIg