Move internal modules to “internal” folder.

.internal/baseSortedIndexBy.js

@@ -0,0 +1,64 @@
+import isSymbol from './isSymbol.js';
+
+/** Used as references for the maximum length and index of an array. */
+const MAX_ARRAY_LENGTH = 4294967295;
+const MAX_ARRAY_INDEX = MAX_ARRAY_LENGTH - 1;
+
+/* Built-in method references for those with the same name as other `lodash` methods. */
+const nativeFloor = Math.floor, nativeMin = Math.min;
+
+/**
+ * The base implementation of `sortedIndexBy` and `sortedLastIndexBy`
+ * which invokes `iteratee` for `value` and each element of `array` to compute
+ * their sort ranking. The iteratee is invoked with one argument; (value).
+ *
+ * @private
+ * @param {Array} array The sorted array to inspect.
+ * @param {*} value The value to evaluate.
+ * @param {Function} iteratee The iteratee invoked per element.
+ * @param {boolean} [retHighest] Specify returning the highest qualified index.
+ * @returns {number} Returns the index at which `value` should be inserted
+ *  into `array`.
+ */
+function baseSortedIndexBy(array, value, iteratee, retHighest) {
+  value = iteratee(value);
+
+  let low = 0;
+  let high = array == null ? 0 : array.length;
+  const valIsNaN = value !== value;
+  const valIsNull = value === null;
+  const valIsSymbol = isSymbol(value);
+  const valIsUndefined = value === undefined;
+
+  while (low < high) {
+    let setLow;
+    const mid = nativeFloor((low + high) / 2);
+    const computed = iteratee(array[mid]);
+    const othIsDefined = computed !== undefined;
+    const othIsNull = computed === null;
+    const othIsReflexive = computed === computed;
+    const othIsSymbol = isSymbol(computed);
+
+    if (valIsNaN) {
+      setLow = retHighest || othIsReflexive;
+    } else if (valIsUndefined) {
+      setLow = othIsReflexive && (retHighest || othIsDefined);
+    } else if (valIsNull) {
+      setLow = othIsReflexive && othIsDefined && (retHighest || !othIsNull);
+    } else if (valIsSymbol) {
+      setLow = othIsReflexive && othIsDefined && !othIsNull && (retHighest || !othIsSymbol);
+    } else if (othIsNull || othIsSymbol) {
+      setLow = false;
+    } else {
+      setLow = retHighest ? (computed <= value) : (computed < value);
+    }
+    if (setLow) {
+      low = mid + 1;
+    } else {
+      high = mid;
+    }
+  }
+  return nativeMin(high, MAX_ARRAY_INDEX);
+}
+
+export default baseSortedIndexBy;