Ciphertext.js

var plaintext = (window.prompt("plaintext:"));

var key = Number(window.prompt("key:"));
var result="";

for(let p of plaintext)
{
  
        if ( p >= 'a' && p <= 'z')
        {
          p = p.charCodeAt();
           p = p - 97;
           p = (p + key) % 26;
           p = p + 97;
           let change = String.fromCharCode(p)
           result += change;
        }
        else if (p >= 'A'&& p<='Z')
        {
        p =p.charCodeAt()
           p = p - 65;
           p = (p + key) % 26;
           p = p + 65;
           let change = String.fromCharCode(p);
           result += change;
        }
    
}
console.log("ciphertext :",result )