Javascript String count(s1)

'use strict';//w  ww.  j a  v a 2  s. c o  m

String.prototype.count = function (s1) {

    return (this.length - this.replace(new RegExp(s1, "g"), '').length) / s1.length;
};

String.prototype.count = function(s1){
  return (this.length - this.replace(new RegExp(s1,"g"), '').length) / s1.length;
}

function countVowels(s){
 var a, e, i, o, u, string;

 s = s.toLowerCase();//from   ww  w.  j a va2  s .  c  om
 a = s.count('a');
 e = s.count('e');
 i = s.count('i');
 o = s.count('o');
 u = s.count('u');
 var total = a+e+i+o+u;
 return "Total: " + total + ' Vowels: a: ' + a + ' e: '+ e + ' i: '+ i + ' o: '+ o + ' u: ' + u;
}

String.prototype.count=function(s1) {   
    return (this.length - this.replace(new RegExp(s1,"g"), '').length) / s1.length;  
}