maxchar.js

// Given a string, return the character that is most
// commonly used in the string.
// --- Examples
// maxChar("abcccccccd") === "c"

function maxChar(str) {
  const charMap = {};
  let max = 0;
  let maxChar = '';

  for (let char of str) {
    if (charMap[char]) {
      charMap[char]++;
    } else {
      charMap[char] = 1;
    }
  }

  for (let char in charMap) {
    if (charMap[char] > max) {
      max = charMap[char];
      maxChar = char;
    }
  }

  return maxChar;
}