I wanna create a recursion to print this pattern with javascript [duplicate]

[50, 41, 32, 23, 14, 5, -4, 5, 14, 23, 32, 41, 50]

I did it but it’s returns undefined!!

let arr = [];
let flag = false;
const recursionPattern = (int1, int2) => {
  if (int1 < 0) {
    flag = true;
  }
  arr.push(int1);
  if (arr[0] == arr[arr.length - 1] && arr.length > 1) return arr;
  else {
    if (flag) recursionPattern(int1 + int2, int2);
    else recursionPattern(int1 - int2, int2);
  }
};