Caesars Cipher any advice?

What do you guys think about my way of coding this project? Any tips or advice on my code? Thank you!

   **Your code so far**
function rot13(str) {
let myCipher = []
let finalCipher=[]
let myArr = str.split("");
let finalArr=[]
for(let i=0; i<myArr.length; i++){
myCipher.push(myArr[i].charCodeAt())
 }
 for(let i=0; i<myCipher.length; i++){
  if(myCipher[i] <78 && myCipher[i] >64) {
   finalCipher.push(myCipher[i] +13)
  }
  else if(myCipher[i]<64){
   finalCipher.push(myCipher[i])
 }  
 else finalCipher.push(myCipher[i] -13)
 }
 for(let i=0; i<finalCipher.length; i++){
   finalArr.push(String.fromCharCode(finalCipher[i]))
 }
 return finalArr.join("").replace(/[-]/g,"")


}
console.log(rot13("SERR YBIR?"));  
   **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36

Challenge: Caesars Cipher

Link to the challenge: