freq.js

freq.js

function freq(s) {
  var r = {}, i, k, c;

  for (i = 0; i < s.length; i++) {
    c = s.charAt(i);

    if (!(c in r)) {
      r[c] = 0;
    }

    r[c]++;
  }

  return r;
}

/* desc */
function cmp(a, b) {
  if (a == b) {
    return 0;
  } else if (a < b) {
    return 1;
  }

  return -1;
}

/**
 * sort([['a', 2], ['b', 1], ['c', 3]], 1)
 *   => [['c', 3], ['a', 2], ['b', 1]]
 */
function sort(a, k) {
  return a.sort(function (a, b) {
    return cmp(a[k], b[k]);
  });
}

function p(s) {
  var f = freq(s), r = [], k;

  for (k in f) {
    r.push([k, f[k]]);
  }

  return sort(r, 1).map(function (a) {
    return a.join(' : ');
  }).join('\n');
}

function main() {
  console.log(p('Hello, world!'));
  /**
   * l : 3
   * o : 2
   * H : 1
   * e : 1
   * , : 1
   *   : 1
   * w : 1
   * r : 1
   * d : 1
   * ! : 1 
   */
}

main()