Javascript String removeSubstring(a, b)

String.prototype.removeSubstring = function(a, b){
 var array = this.split("");
 var w = 0;/*from ww w . j  ava 2  s  .  c  o m*/
 var str = [];
 if (b !== undefined){
  array.forEach(function (elm) {
        if (elm === a & w < b){
          w += 1;
        } else {
         str.push(elm);
        }
     });
 } else {
  array.forEach(function (elm) {
        if (elm !== a){
         str.push(elm);
        }
     });
 }

 return str.toString();;

}

//------------------- Testing -----------------------------------//
var str1 = 'aaaaa';
var newStr1 = str1.removeSubstring('a', 3); // newStr = 'a' 
console.log( newStr1 );
var str2 = 'aaabbbbccc'; 
var newStr2 = str2.removeSubstring('b'); // newStr = 'bbbb' 
console.log( newStr2 );
//------------------- Testing -----------------------------------//