Enhancements to Caesar Cipher Implementation - CaesarCipher.js

Ciphers/CaesarCipher.js

@@ -4,29 +4,42 @@
  * @see - [wiki](https://en.wikipedia.org/wiki/Caesar_cipher)
  * @param  {string} str - string to be encrypted
  * @param {number} rotation - the number of rotation, expect real number ( > 0)
+ * @param {string} [alphabet='abcdefghijklmnopqrstuvwxyz'] - Optional parameter to specify a custom alphabet
  * @return {string} - decrypted string
  */
-const caesarCipher = (str, rotation) => {
+const caesarCipher = (str, rotation, alphabet = 'abcdefghijklmnopqrstuvwxyz') => {
   if (typeof str !== 'string' || !Number.isInteger(rotation) || rotation < 0) {
-    throw new TypeError('Arguments are invalid')
+    throw new TypeError('Arguments are invalid');
   }
 
-  const alphabets = new Array(26)
-    .fill()
-    .map((_, index) => String.fromCharCode(97 + index)) // generate all lower alphabets array a-z
+  const alphabets = Array.from(alphabet); // Allow custom alphabet
+  const alphabetLength = alphabets.length;
 
-  const cipherMap = alphabets.reduce(
-    (map, char, index) => map.set(char, alphabets[(rotation + index) % 26]),
-    new Map()
-  )
+  // Optimize rotation to handle rotations greater than alphabet length
+  const effectiveRotation = rotation % alphabetLength;
+
+  // Create cipher map to avoid recalculating for each character
+  const cipherMap = alphabets.reduce((map, char, index) => {
+    map.set(char, alphabets[(effectiveRotation + index) % alphabetLength]);
+    return map;
+  }, new Map());
 
   return str.replace(/[a-z]/gi, (char) => {
-    if (/[A-Z]/.test(char)) {
-      return cipherMap.get(char.toLowerCase()).toUpperCase()
-    }
+    const isUpperCase = /[A-Z]/.test(char);
+    const lowerChar = char.toLowerCase();
+
+    // Check if the character is in the map (i.e., an alphabetic character)
+    if (cipherMap.has(lowerChar)) {
+      const cipheredChar = cipherMap.get(lowerChar);
+      return isUpperCase ? cipheredChar.toUpperCase() : cipheredChar;
+  }
+
+  return cipherMap.get(char);
+});
+
+};
 
-    return cipherMap.get(char)
-  })
-}
+// Example usage:
+console.log(caesarCipher('Hello World!', 3)); // Khoor Zruog!
 
-export default caesarCipher
+export default caesarCipher;