var arr1 = [1,3,5]
 var arr2 = [4,5]

 var arr3 = []

function sortMergeArray(arr1, arr2) {
  while (arr1.length || arr2.length) {
    var arr1_item = arr1.pop();
    var arr2_item = arr2.pop();
    if (arr1_item <= arr2_item) {
      arr3.push(arr1_item);
      arr2.unshift(arr2_item)
    }
    else {
      arr3.push(arr2_item);
      arr1.unshift(arr1_item)
    }
  }
  return arr3;
}


sortMergeArray(arr1, arr2)