Given range of 1 to N and an array of unique integers that are within that range, return the missing integers not found in the array

missing-number.rb

@arr = [1,3,4] 
@n = 4
@missing_nums = []
  (1..@n).each do |i|
    if !@arr.include?(i)
      @missing_nums.append(i)
    end
   end     
puts @missing_nums      

missingNum.js

arr = [1,3,4] 
n = 4
function missingNumber(n, arr) {
  var missingNums = [];

  for (var i = 1; i <= n; i++) {
    if (!arr.includes(i)) {
      missingNums.push(i);
    }
  }
  return missingNums;
}