Bump to v4.0.0.

findKey.js

@@ -0,0 +1,42 @@
+import baseFind from './internal/baseFind';
+import baseForOwn from './internal/baseForOwn';
+import baseIteratee from './internal/baseIteratee';
+
+/**
+ * This method is like `_.find` except that it returns the key of the first
+ * element `predicate` returns truthy for instead of the element itself.
+ *
+ * @static
+ * @memberOf _
+ * @category Object
+ * @param {Object} object The object to search.
+ * @param {Function|Object|string} [predicate=_.identity] The function invoked per iteration.
+ * @returns {string|undefined} Returns the key of the matched element, else `undefined`.
+ * @example
+ *
+ * var users = {
+ *   'barney':  { 'age': 36, 'active': true },
+ *   'fred':    { 'age': 40, 'active': false },
+ *   'pebbles': { 'age': 1,  'active': true }
+ * };
+ *
+ * _.findKey(users, function(o) { return o.age < 40; });
+ * // => 'barney' (iteration order is not guaranteed)
+ *
+ * // using the `_.matches` iteratee shorthand
+ * _.findKey(users, { 'age': 1, 'active': true });
+ * // => 'pebbles'
+ *
+ * // using the `_.matchesProperty` iteratee shorthand
+ * _.findKey(users, ['active', false]);
+ * // => 'fred'
+ *
+ * // using the `_.property` iteratee shorthand
+ * _.findKey(users, 'active');
+ * // => 'barney'
+ */
+function findKey(object, predicate) {
+  return baseFind(object, baseIteratee(predicate, 3), baseForOwn, true);
+}
+
+export default findKey;