Multiple exercises were added to the TypeScript track in this commit.

typescript/atbash-cipher/atbash-cipher.ts

@@ -0,0 +1,21 @@
+const originalAlphabet = 'abcdefghijklmnopqrstuvwxyz'
+const cipherAlphabet = 'zyxwvutsrqponmlkjihgfedcba'
+
+export function encode(plainText: string): string {
+  return plainText
+    .toLowerCase()
+    .split('')
+    .map(c => c.match(/\d/) ? c : cipherAlphabet[originalAlphabet.indexOf(c)])
+    .filter(Boolean)
+    .map((c, i) =>  (i + 1) % 5 === 0 ? `${c} ` : c)
+    .join("")
+    .trim()
+}
+
+export function decode(cipherText: string): string {
+  return cipherText
+    .split('')
+    .map(c => c.match(/\d/) ? c : originalAlphabet[cipherAlphabet.indexOf(c)])
+    .filter(Boolean)
+    .join("")
+}