| 'use strict'; | 
| var $ = require('../internals/export'); | 
| var aMap = require('../internals/a-map'); | 
| var iterate = require('../internals/map-iterate'); | 
|   | 
| // `Map.prototype.keyOf` method | 
| // https://github.com/tc39/proposal-collection-methods | 
| $({ target: 'Map', proto: true, real: true, forced: true }, { | 
|   keyOf: function keyOf(searchElement) { | 
|     var result = iterate(aMap(this), function (value, key) { | 
|       if (value === searchElement) return { key: key }; | 
|     }, true); | 
|     return result && result.key; | 
|   } | 
| }); |