fungsi hitung kata javascript

  function substr_count(string,substring,start,length)
{
 var c = 0;
 if(start) { string = string.substr(start); }
 if(length) { string = string.substr(0,length); }
 for (var i=0;i<string.length;i++)
 {
  if(substring == string.substr(i,substring.length))
  c++;
 }
 return c;
}
  console.log(substr_count('Your apples are my apples.','apples'))