node_modules

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diff --git a/node_modules/fbjs/lib/_shouldPolyfillES6Collection.js.flow b/node_modules/fbjs/lib/_shouldPolyfillES6Collection.js.flow
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+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule _shouldPolyfillES6Collection
+ * @preventMunge
+ * @flow
+ */
+
+/**
+ * Checks whether a collection name (e.g. "Map" or "Set") has a native polyfill
+ * that is safe to be used.
+ */
+function shouldPolyfillES6Collection(collectionName: string): boolean {
+  const Collection = global[collectionName];
+  if (Collection == null) {
+    return true;
+  }
+
+  // The iterator protocol depends on `Symbol.iterator`. If a collection is
+  // implemented, but `Symbol` is not, it's going to break iteration because
+  // we'll be using custom "@@iterator" instead, which is not implemented on
+  // native collections.
+  if (typeof global.Symbol !== 'function') {
+    return true;
+  }
+
+  const proto = Collection.prototype;
+
+  // These checks are adapted from es6-shim: https://fburl.com/34437854
+  // NOTE: `isCallableWithoutNew` and `!supportsSubclassing` are not checked
+  // because they make debugging with "break on exceptions" difficult.
+  return Collection == null || typeof Collection !== 'function' || typeof proto.clear !== 'function' || new Collection().size !== 0 || typeof proto.keys !== 'function' || typeof proto.forEach !== 'function';
+}
+
+module.exports = shouldPolyfillES6Collection;
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