Javascript String containsPalindrome()

String.prototype.containsPalindrome = function() {
  
 var getCharacterFrequency = function (charArr) {  
  var frequency = {};  
  charArr.forEach(function(c) {
   if (frequency[c]) {
    ++frequency[c];/*  w w w.  ja v a2s .c  om*/
   } else {
    frequency[c] = 1;
   }
  });  
  return frequency;
 }

 var isOddNumber = function (num) {
  return num % 2 !== 0;
 }
 
 var charArr = this.toLowerCase().split("");
 var frequency = getCharacterFrequency(charArr);
 var odds = 0;

 for (const key of Object.keys(frequency)) {
  if (isOddNumber(frequency[key])) {
   if (++odds > 1) {    
    return false;
   }
  }
 }
 
 return true;  
}