Linear version of find all integer inversions

find_inversions.js

function getInversionCount(arr){
  var inv_count = 0;
  var n=arr.length
  for (var i = 0; i < n - 1; i++)
    for (var j = i+1; j < n; j++)
      if (arr[i] > arr[j])
        inv_count++;
  return inv_count;
}


var array=[1,5,4,3,6,12,7,13,8];

var result=getInversionCount(array);
console.log("result "+result)