create project

kitabcitab/node_modules/core-js-pure/modules/esnext.map.group-by.js

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+'use strict';
+var $ = require('../internals/export');
+var call = require('../internals/function-call');
+var uncurryThis = require('../internals/function-uncurry-this');
+var isCallable = require('../internals/is-callable');
+var aCallable = require('../internals/a-callable');
+var iterate = require('../internals/iterate');
+var Map = require('../internals/map-helpers').Map;
+
+var push = uncurryThis([].push);
+
+// `Map.groupBy` method
+// https://github.com/tc39/proposal-collection-methods
+$({ target: 'Map', stat: true, forced: true }, {
+  groupBy: function groupBy(iterable, keyDerivative) {
+    var C = isCallable(this) ? this : Map;
+    var newMap = new C();
+    aCallable(keyDerivative);
+    var has = aCallable(newMap.has);
+    var get = aCallable(newMap.get);
+    var set = aCallable(newMap.set);
+    iterate(iterable, function (element) {
+      var derivedKey = keyDerivative(element);
+      if (!call(has, newMap, derivedKey)) call(set, newMap, derivedKey, [element]);
+      else push(call(get, newMap, derivedKey), element);
+    });
+    return newMap;
+  }
+});