Solution

src/formatDate.js

@@ -8,7 +8,37 @@
  * @returns {string}
  */
 function formatDate(date, fromFormat, toFormat) {
-  // write code here
+  const result = [];
+  const separator = fromFormat[fromFormat.length - 1];
+  const parts = date.split(separator);
+  const mapping = {};
+
+  for (let i = 0; i < fromFormat.length - 1; i++) {
+    mapping[fromFormat[i]] = parts[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);
+
+    if (year < 30) {
+      mapping['YYYY'] = 20 + mapping['YY'];
+    } else {
+      mapping['YYYY'] = 19 + mapping['YY'];
+    }
+  }
+
+  const newSeparator = toFormat[toFormat.length - 1];
+
+  const newDate = toFormat
+    .slice(0, -1)
+    .map((format) => mapping[format])
+    .join(newSeparator);
+
+  result.push(newDate);
+
+  return result.join('');
 }
 
 module.exports = formatDate;