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

79 lines
2.2 KiB
JavaScript

/**
* @generated SignedSource<<6c1a82d2f5918f03f3f0e5825e1f32f3>>
*
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
* !! 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 2013-2014 Facebook, Inc.
* @providesModule _shouldPolyfillES6Collection
* @preventMunge
* @typechecks
*/
/**
* Given a collection class name (Map or Set) return whether it's safe to use
* the native polyfill.
*
* @param {string} collectionName
*/
function shouldPolyfillES6Collection(collectionName) {
var Collection = global[collectionName];
if (Collection == null) {
return true;
}
var proto = Collection.prototype;
// These checks are adapted from es6-shim https://fburl.com/34437854
return Collection == null ||
typeof Collection !== 'function' ||
typeof proto.clear !== 'function' ||
new Collection().size !== 0 ||
typeof proto.keys !== 'function' ||
typeof proto.forEach !== 'function' ||
isCallableWithoutNew(Collection) ||
!supportsSubclassing(Collection);
}
/**
* Given a class can we subclass it?
*
* @param {function} Collection
*/
function supportsSubclassing(Collection) {
class SubCollection extends Collection {}
try {
var s = (new SubCollection([]));
// Firefox 32 will throw a type error when any operation is called on a
// subclass.
s.size;
return s instanceof Collection;
} catch (e) {
return false;
}
}
/**
* Given a constructor can we call it without `new`?
*
* @param {function} Collection
*/
function isCallableWithoutNew(Collection) {
try {
Collection();
} catch (e) {
return false;
}
return true;
}
module.exports = shouldPolyfillES6Collection;