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)
// The `_.matches` iteratee shorthand. _.findKey(users, { 'age': 1, 'active': true }); // => 'pebbles'
// The `_.matchesProperty` iteratee shorthand. _.findKey(users, ['active', false]); // => 'fred'
// The `_.property` iteratee shorthand. _.findKey(users, 'active'); // => 'barney'