Solution

src/formatDate.js

@@ -8,7 +8,51 @@
  * @returns {string}
  */
 function formatDate(date, fromFormat, toFormat) {
-  // write code here
+  const separator = fromFormat.at(-1);
+  const dateParts = date.split(separator);
+
+  const yearIndex = fromFormat.includes('YYYY')
+    ? fromFormat.indexOf('YYYY')
+    : fromFormat.indexOf('YY');
+  let year = dateParts[yearIndex];
+
+  const monthIndex = fromFormat.indexOf('MM');
+  const month = dateParts[monthIndex];
+
+  const dayIndex = fromFormat.indexOf('DD');
+  const day = dateParts[dayIndex];
+
+  if (year.length === 2) {
+    if (Number(year) < 30) {
+      year = '20' + year;
+    } else {
+      year = '19' + year;
+    }
+  }
+
+  if (year.length === 4 && toFormat.includes('YY')) {
+    year = year.slice(-2);
+  }
+
+  const resultParts = [];
+
+  for (let i = 0; i < 3; i++) {
+    if (toFormat[i] === 'DD') {
+      resultParts.push(day);
+    }
+
+    if (toFormat[i] === 'MM') {
+      resultParts.push(month);
+    }
+
+    if (toFormat[i] === 'YYYY' || toFormat[i] === 'YY') {
+      resultParts.push(year);
+    }
+  }
+
+  const newSeparator = toFormat.at(-1);
+
+  return resultParts.join(newSeparator);
 }
 
 module.exports = formatDate;