JavaScript Interview Question: Find all Vowels in a string

vowel.js

/*
  Create a function to return the total number of vowels in a string.
  
  Use String.prototype.match() to find matches
  using a regular expression. 
  
  /[aeiou]/gi
  
  //    denotes a regex pattern.
  []    instructs match() to find any of these characters.
  g     instructs match() to search globally in the string 
        and return all matches.
  i     instructs match() to be case insensitive. 
  
  String.prototype.match() returns an array of 
  matches or null when no match is found. We can 
  return the total count by using a ternary operator. 
  
  If matches() returns an array, this is
  considered truthy, therefore, we return the length
  of the array. If matches() returns null, this is
  considered falsy, therefore, we need to return 0.
*/

function vowel(str) {
  const matches = str.match(/[aeiou]/gi);
  return matches ? matches.length : 0;
}

//Try it
console.log(vowel('abcdefg')); // Returns 2

word-with-most-vowels.js

//Find and return the word with the highest frequency of vowels in a string of text.

function vowels(str) {
  //Create an object with key/value pairs containing word (key) and vowel count (value).
  const wordMap = getVowelFrequencyMap(str);
  
  //Use reduce as a comparator to return the word with the most vowels.
  return Object.keys(wordMap).reduce((a,b) => wordMap[a] > wordMap[b] ? a : b);
}

//Helper function to get the character frequency.
function getVowelFrequencyMap(str) {
  let map = {};
  str.split(' ').forEach(word => {
    let matches = word.match(/[aeiou]/gi);
    map[word] = matches ? matches.length : 0;
  });
  
  return map;
}

//Try it
console.log(`Word with most vowels: ${vowels('Goodnight Moon')}`);