Apply let/const transform.

_baseIndexOfWith.js

@@ -9,8 +9,8 @@
  * @returns {number} Returns the index of the matched value, else `-1`.
  */
 function baseIndexOfWith(array, value, fromIndex, comparator) {
-  var index = fromIndex - 1,
-      length = array.length;
+  let index = fromIndex - 1;
+  const length = array.length;
 
   while (++index < length) {
     if (comparator(array[index], value)) {