esnext.map.key-of.js

'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;
  }
});