--- /dev/null
+var arrayPush = require('./arrayPush'),
+ isArguments = require('../lang/isArguments'),
+ isArray = require('../lang/isArray'),
+ isArrayLike = require('./isArrayLike'),
+ isObjectLike = require('./isObjectLike');
+
+/**
+ * The base implementation of `_.flatten` with added support for restricting
+ * flattening and specifying the start index.
+ *
+ * @private
+ * @param {Array} array The array to flatten.
+ * @param {boolean} [isDeep] Specify a deep flatten.
+ * @param {boolean} [isStrict] Restrict flattening to arrays-like objects.
+ * @param {Array} [result=[]] The initial result value.
+ * @returns {Array} Returns the new flattened array.
+ */
+function baseFlatten(array, isDeep, isStrict, result) {
+ result || (result = []);
+
+ var index = -1,
+ length = array.length;
+
+ while (++index < length) {
+ var value = array[index];
+ if (isObjectLike(value) && isArrayLike(value) &&
+ (isStrict || isArray(value) || isArguments(value))) {
+ if (isDeep) {
+ // Recursively flatten arrays (susceptible to call stack limits).
+ baseFlatten(value, isDeep, isStrict, result);
+ } else {
+ arrayPush(result, value);
+ }
+ } else if (!isStrict) {
+ result[result.length] = value;
+ }
+ }
+ return result;
+}
+
+module.exports = baseFlatten;