Solution

src/formatDate.js

@@ -8,7 +8,31 @@
  * @returns {string}
  */
 function formatDate(date, fromFormat, toFormat) {
-  // write code here
+  const [fromParts, separator] = [fromFormat.slice(0, -1), fromFormat[3]];
+  const [toParts, separatorNew] = [toFormat.slice(0, -1), toFormat[3]];
+  const dateParts = date.split(separator);
+  const dateFrom = {};
+  const dateTo = [];
+
+  for (let i = 0; i < fromParts.length; i++) {
+    dateFrom[fromParts[i]] = dateParts[i];
+  }
+
+  if (dateFrom.YYYY) {
+    dateFrom.YY = dateFrom.YYYY.slice(-2);
+  } else if (dateFrom.YY) {
+    if (dateFrom.YY < 30) {
+      dateFrom.YYYY = `20${dateFrom.YY}`;
+    } else {
+      dateFrom.YYYY = `19${dateFrom.YY}`;
+    }
+  }
+
+  for (let i = 0; i < toParts.length; i++) {
+    dateTo.push(dateFrom[toParts[i]]);
+  }
+
+  return dateTo.join(separatorNew);
 }
 
 module.exports = formatDate;