function primeFactors(n){
  var factors = [], 
      divisor = 2;
  
  while(n>=2){
    if(n % divisor == 0){
       factors.push(divisor); 
       n= n/ divisor;
    }
    else{
      divisor++;
    }     
  }
    //contains duplicates, you should Array.prototype.filter() them out
  return factors;
}