Grokking

function getTokens(rawString) {
  // NB: `.filter(Boolean)` removes any falsy items from an array
  // returns an array of strings. splits it by symbols and spaces and has been sorted.
  return rawString.toLowerCase().split(/[ ,!.";:-]+/).filter(Boolean).sort();
}

// text is a body of text like a paragraph from a novel, or song lyrics
function mostFrequentWord(text) {
  // declares words and passes text to the function getTokens() and returns it as an array of strings.
  let words = getTokens(text);
  // creates an empty object
  let wordFrequencies = {};
  // loops through the whole array of words
  for (let i = 0; i <= words.length; i++) {
    // check to see if word at index i is in wordFrequencies object
    if (words[i] in wordFrequencies) {
      // if word is already in wordFrequencies class adds +1 to the counter
      wordFrequencies[words[i]]++;
    } else {
      // if the current word is not in the wordFrequencies class create a counter and set it to 1
      wordFrequencies[words[i]] = 1;
    }
  }
  // sets the currentMaxKey to the first string in the array
  let currentMaxKey = Object.keys(wordFrequencies)[0];
  // sets currentMaxCount to the 
  let currentMaxCount = wordFrequencies[currentMaxKey];
  // go through each word in the class wordFrequencies to find the greatest
  for (let word in wordFrequencies) {
    // if this word count is greater than currentMaxCount set the Key and Counter to the currnet
    if (wordFrequencies[word] > currentMaxCount) {
      currentMaxKey = word;
      currentMaxCount = wordFrequencies[word];
    }
  }
  // return the word with the greates word count
  return currentMaxKey;
}