Permutation Average.js

/*
Description:
A number is simply made up of digits.
The number 1256 is made up of the digits 1, 2, 5, and 6.
For 1256 there are 24 distinct permuations of the digits:
1256, 1265, 1625, 1652, 1562, 1526, 2156, 2165, 2615, 2651, 2561, 2516,
5126, 5162, 5216, 5261, 5621, 5612, 6125, 6152, 6251, 6215, 6521, 6512.

Your goal is to write a program that takes a number, n, and returns the average value of all distinct permutations of the digits in n. Your answer should be rounded to the nearest integer. For the example above the return value would be 3889.

n will never be negative

A few examples:

permutation_average(2)
return 2

permutation_average(25)
>>> 25 + 52 = 77
>>> 77 / 2 = 38.5
return 39

permutation_average(20)
>>> 20 + 02 = 22
>>> 22 / 2 = 11
return 11

permutation_average(737)
>>> 737 + 377 + 773 = 1887
>>> 1887 / 3 = 629
return 629

Note: Your program should be able to handle numbers up to 6 digits long
*/
function permutationAverage(n){
  let arr=[];
  let str=n.toString().split('');
  for (let i = 0; i < str.length; i++) {
        arr.push( rotLeft(str,str.length-i).join('')*1)
     }
  return Math.round(arr.reduce((a,b)=>a+b,0)/arr.length)
}
function rotLeft(arr, n) {
     let arrTemp = arr.map(v=>v);
     for (let i = 0; i < n; i++) {
         let temp = arrTemp.shift()
        arrTemp.push(temp)
     }
    return arrTemp
}