--- /dev/null
+'use strict';
+require('../../modules/es.map');
+require('../../modules/esnext.map.key-by');
+var path = require('../../internals/path');
+
+var Map = path.Map;
+var mapKeyBy = Map.keyBy;
+
+module.exports = function keyBy(source, iterable, keyDerivative) {
+ return mapKeyBy.call(typeof this === 'function' ? this : Map, source, iterable, keyDerivative);
+};