[Algorithm] Max Chars Problem

// --- Directions
// Given a string, return the character that is most
// commonly used in the string.
// --- Examples
// maxChar("abcccccccd") === "c"
// maxChar("apple 1231111") === "1"

function maxChar(str) {
  let m = {},
    max = -1,
    result = null;

  for (let char of str) {
    m[char] = m[char] + 1 || 1;
  }

  for (let [key, count] of Object.entries(m)) {
    max = Math.max(max, count);
    if (max === count) {
      result = key;
    }
  }

  return result;
}

module.exports = maxChar;

　　

const maxChar = require('./index');

test('maxChar function exists', () => {
  expect(typeof maxChar).toEqual('function');
});

test('Finds the most frequently used char', () => {
  expect(maxChar('a')).toEqual('a');
  expect(maxChar('abcdefghijklmnaaaaa')).toEqual('a');
});

test('Works with numbers in the string', () => {
  expect(maxChar('ab1c1d1e1f1g1')).toEqual('1');
});