How deep do these trees even go?

how-deep-do-these-trees-even-go/index.js

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+// https://www.codewars.com/kata/how-deep-do-these-trees-even-go/train/javascript
+
+function arrayDeepness(arr) {
+  let deep = (arr, lvl, fn) => {
+    if (arr && arr.map) {
+//       arr.map(el => deep(el, lvl + 1, fn));
+      for (let i = 0; i < arr.length; ++i) {
+        deep(arr[i], lvl + 1, fn);
+      }
+    } else {
+      fn(lvl);
+    }
+  };
+  let res = [];
+  deep(arr, 0, lvl => res.push(lvl));
+  let min = Math.min(...res);
+  let max = Math.max(0, ...res);
+  let mean = +(res.reduce((a, b) => a + b, 0) / res.length).toFixed(3);
+  return {min, max, mean};
+}