I would personally use test() to test my strings: MDN test()
This will simply test a string to see if it matches a regex pattern.
Another tool which will really help you is RegexPal: Regex Pal
This will make it a lot easier for you to see what you regexes are doing without having to run the code.
Your vowel regex should only include vowels as mentioned by @ilenia. So your vowel regex should be /[aeiou]/
In order to find the position of a vowel it might useful for you to use a for loop. This will allow you to test each character of a string against your regex, systematically: MDN For Of Loop
The example I have included below demonstrates how a for of loop can iterate over a string and return the index of the first vowel: