refactor: improving readability for flat function

3.implement-Array.prototype.flat.md

@@ -35,17 +35,17 @@ Are you able to solve it both recursively and iteratively?
  * @param { Array } arr
  * @param { number } depth
  */
-function flat(arr, depth = 1) {
+const flat = (array, depth = 1) => {
   let flatArray = [];
-  for (const item of arr) {
-    if (Array.isArray(item) && depth > 0) {
-      flatArray = flatArray.concat(flat(item, depth - 1));
+  array.forEach((element) => {
+    if (Array.isArray(element) && depth > 0) {
+      flatArray.push(...flat(element, depth - 1));
     } else {
-      flatArray.push(item);
+      flatArray.push(element);
     }
-  }
+  });
   return flatArray;
-}
+};
 ```
 
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