Update sortedLastIndexBy.md

snippets/sortedLastIndexBy.md

@@ -3,16 +3,17 @@
 Returns the highest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
 
 Check if the array is sorted in descending order (loosely).
-Use `Array.reverse()` and `Array.findIndex()` to find the appropriate last index where the element should be inserted, based on the iterator function `fn`..
+Use `Array.map()` to apply the iterator function to all elements of the array.
+Use `Array.reverse()` and `Array.findIndex()` to find the appropriate last index where the element should be inserted, based on the provided iterator function.
 
 ```js
 const sortedLastIndexBy = (arr, n, fn) => {
   const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
   const val = fn(n);
   const index = arr
-    .map((val, i) => [i, fn(val)])
+    .map(fn)
     .reverse()
-    .findIndex(el => (isDescending ? val <= el[1] : val >= el[1]));
+    .findIndex(el => (isDescending ? val <= el : val >= el));
   return index === -1 ? 0 : arr.length - index;
 };
 ```