const charFrequency = (string) => {
  let count = {};
  let results = [];
  string.split('').forEach(function(c) {
    count[c] ? count[c] += 1 : count[c] = 1;
    
  });
  var keys = Object.keys(count);
  keys.forEach(function(key) {
    results.push([key, count[key]])
  });
  
  return results
}

// const concatMap = (array, fn) => {
//     return array.map(function(el) {
//         return fn(el);
//     }).concatAll();
// };
///\\// sort descending order by FREQUENCY\\
const sortDescByFreq = (a, b) => {
  if (a > b) {
    return 1;
  }
  if (a < b) {
    return -1;
  }
  return 0;
};

const sortAscByChar = (a, b) => { ///// then sort by ASCENDING order character
    return a - b;
}




var countMississippi = charFrequency("mississippi");

var sortedByFreq = countMississippi.sort(sortDescByFreq());




var sortedByChar = sortedByFreq.sort(sortAscByChar(a, b))


// [ [ "i", 4 ], [ "s", 4 ], [ "p", 2 ], [ "m", 1 ] ]