Solution

src/formatDate.js

@@ -8,7 +8,29 @@
  * @returns {string}
  */
 function formatDate(date, fromFormat, toFormat) {
-  // write code here
+  const fromSeparator = fromFormat.pop();
+  const toSeparator = toFormat.pop();
+  const dateParts = date.split(fromSeparator);
+
+  const mapping = {};
+
+  for (let i = 0; i < fromFormat.length; i++) {
+    const key = fromFormat[i];
+
+    mapping[key] = dateParts[i];
+  }
+
+  if (fromFormat.includes('YYYY') && toFormat.includes('YY')) {
+    mapping['YY'] = mapping['YYYY'].slice(-2);
+  } else if (fromFormat.includes('YY') && toFormat.includes('YYYY')) {
+    const year = parseInt(mapping['YY'], 10);
+
+    mapping['YYYY'] = year < 30 ? `20${mapping['YY']}` : `19${mapping['YY']}`;
+  }
+
+  const result = toFormat.map((part) => mapping[part]).join(toSeparator);
+
+  return result;
 }
 
 module.exports = formatDate;