JavaScript Algorithms and Data Structures Projects - Caesars Cipher

Tell us what’s happening:
Hi, My second for loop is reversing the changes made in my first loop. Why is that?
Your code so far

function rot13(str) {

  let rot1 = [ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M' ];
  let rot2 = [ 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' ];
  let newArr = str.split("")
  let newStr = newArr;
  

  // If number letter in str is equal to a letter in rot1 array than change that letter to a letter in rot2 with the same index as rot1.
   for (let i = 0; i < newStr.length; i++){
     for (let j = 0; j < rot1.length; j++){
      if(rot1[j] === newStr[i]){
       newStr[i] = rot2[j]
      }
     }
    }

 // If number letter in str is equal to a letter in rot2 array than change that letter to a letter in rot1 with the same index as rot2.
    for (let i = 0; i < newStr.length; i++){
     for (let k = 0; k < rot2.length; k++){
      if(rot2[k] === newStr[i]){
        newStr[i] = rot1[k]
      }
     }
    }

return newStr
}

let result = rot13("SERR CVMMN!");
console.log(result)

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Challenge: JavaScript Algorithms and Data Structures Projects - Caesars Cipher

Link to the challenge:

The answer is in your comments.
The first loop takes all the characters that match with rot1 and makes them shifted to rot2.
While the second loop reversed that by changing all the characters back.

I think you need to consider using the ASCII table to find a solution for this.