Caesar Cipher

caesarCipher.js

// Assumptions:
// All input characters that are uppercase should remain toUpperCase
// Non-alphabetical characters should remain the same

// Only check for non-uppercase vowels to capitalize
const vowels = ['a', 'e', 'i', 'o', 'u'];

// Helper function
const isVowel = char => vowels.includes(char);

const asciiShift = (input) => {
  let shiftedString = '';

  // iterate through input
  const inputLength = input.length;
  for (let i = 0; i < inputLength; i++) {
    // only change alphabetical characters
    if (input[i].match(/[a-zA-Z]/i)) {
      // for each character, convert to ascii
      const charToAscii = input.charCodeAt(i);

      let newAsciiChar;

      // if the character is uppercase
      if ((charToAscii >= 65) && (charToAscii <= 90)) {
        // characters at the end of the uppercase range should
        // wrap to the beginning of the range
        newAsciiChar = String.fromCharCode(((charToAscii - 65 + 1) % 26) + 65);
      // the character is lowercase
      } else if ((charToAscii >= 97) && (charToAscii <= 122)) {
        newAsciiChar = String.fromCharCode(((charToAscii - 97 + 1) % 26) + 97);
      }

      // append new character to temp string
      shiftedString += newAsciiChar;
    } else {
      // append non-alphabetical characters as-is
      shiftedString += input[i];
    }
  }

  let outputString = '';

  // iterate through temp string
  for (let k = 0; k < inputLength; k++) {
    const currentChar = shiftedString[k];

    // if the character is a vowel, capitalize it and append to output string
    if (isVowel(currentChar)) {
      outputString += shiftedString[k].toUpperCase();
    // else append to string
    } else {
      outputString += shiftedString[k];
    }
  }

  return(outputString);
}

const testString = 'Hello Annette!';

console.log(asciiShift(testString));

// Potential tests:
// Input and output are the same length
// Non-alphabetical characters remain at the same indices in input and output