Count Integer Inversions by modifying merge sort

Inversions.js

class Inversioncount{

    constructor(numbers){
     this.numbers=numbers;
     this.count=0;
    }

  merge(left, right){
    var result=[];

   ///Conquer
   while (left.length && right.length ) {
    if (left[0] <= right[0]) {
       result.push(left.shift());
    } else {
       this.count++;
        result.push(right.shift());
    }
   }


   //Process into a result
    while (left.length)
       result.push(left.shift());

    while (right.length)
       result.push(right.shift());


      console.log(result);

    return result;
  }

  mergesort(array){
     //If the array size is 0 or 1 return the array
     if(array.length <2)
        return array;

    //Divide
     var middle = parseInt(array.length /2);
     var left = array.slice(0,middle);
     var right= array.slice(middle,array.length)

     return this.merge(this.mergesort(left),this.mergesort(right));
   }


  sort(){
    this.mergesort(this.numbers);
    console.log("The count:"+this.count);
  }


}


var numbers=[1,2,3,5,4]

sort=new Inversioncount(numbers);
sort.sort();