lodash/object/findKey.js

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;