79 lines
2.2 KiB
JavaScript
79 lines
2.2 KiB
JavaScript
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/**
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* @generated SignedSource<<6c1a82d2f5918f03f3f0e5825e1f32f3>>
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*
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* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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* !! This file is a check-in of a static_upstream project! !!
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* !! !!
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* !! You should not modify this file directly. Instead: !!
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* !! 1) Use `fjs use-upstream` to temporarily replace this with !!
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* !! the latest version from upstream. !!
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* !! 2) Make your changes, test them, etc. !!
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* !! 3) Use `fjs push-upstream` to copy your changes back to !!
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* !! static_upstream. !!
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* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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*
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* Copyright 2013-2014 Facebook, Inc.
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* @providesModule _shouldPolyfillES6Collection
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* @preventMunge
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* @typechecks
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*/
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/**
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* Given a collection class name (Map or Set) return whether it's safe to use
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* the native polyfill.
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*
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* @param {string} collectionName
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*/
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function shouldPolyfillES6Collection(collectionName) {
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var Collection = global[collectionName];
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if (Collection == null) {
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return true;
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}
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var proto = Collection.prototype;
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// These checks are adapted from es6-shim https://fburl.com/34437854
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return Collection == null ||
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typeof Collection !== 'function' ||
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typeof proto.clear !== 'function' ||
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new Collection().size !== 0 ||
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typeof proto.keys !== 'function' ||
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typeof proto.forEach !== 'function' ||
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isCallableWithoutNew(Collection) ||
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!supportsSubclassing(Collection);
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}
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/**
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* Given a class can we subclass it?
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*
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* @param {function} Collection
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*/
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function supportsSubclassing(Collection) {
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class SubCollection extends Collection {}
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try {
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var s = (new SubCollection([]));
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// Firefox 32 will throw a type error when any operation is called on a
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// subclass.
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s.size;
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return s instanceof Collection;
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} catch (e) {
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return false;
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}
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}
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/**
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* Given a constructor can we call it without `new`?
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*
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* @param {function} Collection
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*/
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function isCallableWithoutNew(Collection) {
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try {
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Collection();
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} catch (e) {
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return false;
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}
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return true;
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}
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module.exports = shouldPolyfillES6Collection;
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