my-string-class.js

function MyStringClass(str) {
  var map = {};

  // front-load the work and has the string
  for (var i = 0; i < str.length; i++) {
    var char = str[i];
    map[char] = map[char] || 0;
    map[char]++;
  }

  this.getCount = function (c) {
    return map[c] || 0;
  };

  this.getMost = function () {
    var max = 0;
    var results = [];
    Object.keys(map).forEach(function (c) {
      if (map[c] > max) {
        max = map[c];
        results = [c];
      } else if (map[c] === max) {
        results.push(c);
      }
    });
    return results;
  }
}


var foo = new MyStringClass('racecar');

console.log(foo.count('a')); // => 2
console.log(foo.most()); // => ['a', 'c', 'r'] (non-deterministic order)

rewritten in a "classier" way rather than as an obj factory