Bump to v3.0.0.

object/findKey.js

@@ -0,0 +1,49 @@
+import baseCallback from '../internal/baseCallback';
+import baseFind from '../internal/baseFind';
+import baseForOwn from '../internal/baseForOwn';
+
+/**
+ * This method is like `_.findIndex` except that it returns the key of the
+ * first element `predicate` returns truthy for, instead of the element itself.
+ *
+ * If a property name is provided for `predicate` the created "_.property"
+ * style callback returns the property value of the given element.
+ *
+ * If an object is provided for `predicate` the created "_.matches" style
+ * callback returns `true` for elements that have the properties of the given
+ * object, else `false`.
+ *
+ * @static
+ * @memberOf _
+ * @category Object
+ * @param {Object} object The object to search.
+ * @param {Function|Object|string} [predicate=_.identity] The function invoked
+ *  per iteration. If a property name or object is provided it is used to
+ *  create a "_.property" or "_.matches" style callback respectively.
+ * @param {*} [thisArg] The `this` binding of `predicate`.
+ * @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(chr) { return chr.age < 40; });
+ * // => 'barney' (iteration order is not guaranteed)
+ *
+ * // using the "_.matches" callback shorthand
+ * _.findKey(users, { 'age': 1 });
+ * // => 'pebbles'
+ *
+ * // using the "_.property" callback shorthand
+ * _.findKey(users, 'active');
+ * // => 'barney'
+ */
+function findKey(object, predicate, thisArg) {
+  predicate = baseCallback(predicate, thisArg, 3);
+  return baseFind(object, predicate, baseForOwn, true);
+}
+
+export default findKey;