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function getTokens(rawString) {
  // NB: `.filter(Boolean)` removes any falsy items from an array
  
  // this function takes a string as an argument, changes all letters to
  // lowercase, and splits the string when it encounters at least one of
  // these punctuation marks: ,!.";:-
  // then the string is filtered as described above and sorted by unicode values.
  
  return rawString.toLowerCase().split(/[ ,!.";:-]+/).filter(Boolean).sort();
}

function mostFrequentWord(text) {
  // initialize variables to be used later
  
  // words is an array of strings created by getTokens()
  let words = getTokens(text);
  
  // this will contain the appearance count of each word
  let wordFrequencies = {};
  
  // loop through the array of words created earlier, and...
  for (let i = 0; i <= words.length; i++) {
    if (words[i] in wordFrequencies) {
      // ...if a word already exists in the wordFrequencies object,
      // increase its appearance count.
      wordFrequencies[words[i]]++;
    } else {
      // ...if a word is appearing in the array for the first time,
      // add it to the wordFrequencies object and set its count to 1.
      wordFrequencies[words[i]] = 1;
    }
  }
  
  // currentMaxKey is the first word in the wordFrequencies object
  // and currentMaxCount is the appearance count of that word.
  let currentMaxKey = Object.keys(wordFrequencies)[0];
  let currentMaxCount = wordFrequencies[currentMaxKey];

  // loop through the wordFrequencies object we created, and...
  for (let word in wordFrequencies) {
    if (wordFrequencies[word] > currentMaxCount) {
    
      // ...if the word in the current iteration has a larger appearance count
      // than the current word with the largest appearance count,
      // set that word to be the new word with the most appearances.
      // do this until the word with the largest count overall is in currentMaxKey.
      currentMaxKey = word;
      currentMaxCount = wordFrequencies[word];
    }
  }
  
  // return the word with the most appearances.
  return currentMaxKey;
}