Move internal modules to “internal” folder.

.internal/baseIndexOf.js

@@ -0,0 +1,20 @@
+import baseFindIndex from './.internal/baseFindIndex.js';
+import baseIsNaN from './.internal/baseIsNaN.js';
+import strictIndexOf from './.internal/strictIndexOf.js';
+
+/**
+ * The base implementation of `indexOf` without `fromIndex` bounds checks.
+ *
+ * @private
+ * @param {Array} array The array to inspect.
+ * @param {*} value The value to search for.
+ * @param {number} fromIndex The index to search from.
+ * @returns {number} Returns the index of the matched value, else `-1`.
+ */
+function baseIndexOf(array, value, fromIndex) {
+  return value === value
+    ? strictIndexOf(array, value, fromIndex)
+    : baseFindIndex(array, baseIsNaN, fromIndex);
+}
+
+export default baseIndexOf;