react-native/Libraries/vendor/core/_shouldPolyfillES6Collectio...

54 lines
2.0 KiB
JavaScript

/**
* @generated SignedSource<<bf0749e529897a7c9687fff37310d4d2>>
*
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
* !! This file is a check-in of a static_upstream project! !!
* !! !!
* !! You should not modify this file directly. Instead: !!
* !! 1) Use `fjs use-upstream` to temporarily replace this with !!
* !! the latest version from upstream. !!
* !! 2) Make your changes, test them, etc. !!
* !! 3) Use `fjs push-upstream` to copy your changes back to !!
* !! static_upstream. !!
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*
* Copyright 2004-present Facebook. All Rights Reserved.
*
* @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 {
var 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;
}
var 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;