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