one of the simplest and most widely known encryption techniques.

caesarCipher.js

/**
 * Returns the result of having each alphabetic letter of the given text string shifted forward
 * by the given amount, with wraparound. Case is preserved, and non-letters are unchanged.
 *
 * i.e.
 * 
 * - caesarShift({ text: "abz", shift: 0 }) = "abz".
 * - caesarShift({ text: "abz", shift: 1 }) = "bca".
 * - caesarShift({ text: "abz", shift: 25 }) = "zay".
 * - caesarShift({ text: "THe 123 !@#$", shift: 13 }) = "GUr 123 !@#$".
**/

const caesarShift = ({ text, shift }) => {
  let result = '';

  for (var i = 0; i < text.length; i++) {
    let c = text.charCodeAt(i);

    if (65 <= c && c <= 90) {
      result += String.fromCharCode((c - 65 + shift) % 26 + 65);  // Uppercase
    } else if (97 <= c && c <= 122) {
      result += String.fromCharCode((c - 97 + shift) % 26 + 97);  // Lowercase
    } else {
      result += text.charAt(i);  // Copy
    }
  }

  return result;
}