Bump to v4.9.0.

_baseFlatten.js

@@ -1,7 +1,5 @@
 var arrayPush = require('./_arrayPush'),
-    isArguments = require('./isArguments'),
-    isArray = require('./isArray'),
-    isArrayLikeObject = require('./isArrayLikeObject');
+    isFlattenable = require('./_isFlattenable');
 
 /**
  * The base implementation of `_.flatten` with support for restricting flattening.
@@ -9,23 +7,24 @@ var arrayPush = require('./_arrayPush'),
  * @private
  * @param {Array} array The array to flatten.
  * @param {number} depth The maximum recursion depth.
- * @param {boolean} [isStrict] Restrict flattening to arrays-like objects.
+ * @param {boolean} [predicate=isFlattenable] The function invoked per iteration.
+ * @param {boolean} [isStrict] Restrict to values that pass `predicate` checks.
  * @param {Array} [result=[]] The initial result value.
  * @returns {Array} Returns the new flattened array.
  */
-function baseFlatten(array, depth, isStrict, result) {
-  result || (result = []);
-
+function baseFlatten(array, depth, predicate, isStrict, result) {
   var index = -1,
       length = array.length;
 
+  predicate || (predicate = isFlattenable);
+  result || (result = []);
+
   while (++index < length) {
     var value = array[index];
-    if (depth > 0 && isArrayLikeObject(value) &&
-        (isStrict || isArray(value) || isArguments(value))) {
+    if (depth > 0 && predicate(value)) {
       if (depth > 1) {
         // Recursively flatten arrays (susceptible to call stack limits).
-        baseFlatten(value, depth - 1, isStrict, result);
+        baseFlatten(value, depth - 1, predicate, isStrict, result);
       } else {
         arrayPush(result, value);
       }