stuff

buildfiles/node_modules/core-js/modules/esnext.map.key-by.js

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+'use strict';
+var $ = require('../internals/export');
+var iterate = require('../internals/iterate');
+var aFunction = require('../internals/a-function');
+
+// `Map.keyBy` method
+// https://github.com/tc39/proposal-collection-methods
+$({ target: 'Map', stat: true }, {
+  keyBy: function keyBy(iterable, keyDerivative) {
+    var newMap = new this();
+    aFunction(keyDerivative);
+    var setter = aFunction(newMap.set);
+    iterate(iterable, function (element) {
+      setter.call(newMap, keyDerivative(element), element);
+    });
+    return newMap;
+  }
+});