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/**
* Copyright (c) 2013-present, Facebook, Inc.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*
* @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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