return default index when not found

snippets/findLastIndex.md

@@ -4,15 +4,17 @@ Returns the index of the last element for which the provided function returns a
 
 Use `Array.prototype.map()` to map each element to an array with its index and value.
 Use `Array.prototype.filter()` to remove elements for which `fn` returns falsy values, `Array.prototype.pop()` to get the last one.
+`-1` is the default value when not found.
 
 ```js
 const findLastIndex = (arr, fn) =>
-  arr
+  (arr
     .map((val, i) => [i, val])
     .filter(([i, val]) => fn(val, i, arr))
-    .pop()[0];
+    .pop() || [-1])[0];
 ```
 
 ```js
 findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)
+findLastIndex([1, 2, 3, 4], n => n === 5); // -1 (default value when not found)
 ```