dupesCount.js

function duplicateCount(text) {
  const tracker = {};
  const dupes = [];

  for (const char of text.toLowerCase()) {
    if (tracker.hasOwnProperty(char)) {
      tracker[char]++;
    } else {
      tracker[char] = 1;
    }
  }

  for (const prop in tracker) {
    if(tracker[prop] > 1) dupes.push(prop);
  }

  return dupes.length;
}