Bad Map Polyfill In React Code

React's BadMapPolyfill.js checks if Map polyfills are used, setting hasBadMapPolyfill to true if it fails. This is done in ReactFiber.js.

In this article, we study the packages/react/src/BadMapPolyfill.js file source code.

/**
 * Copyright © Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 * @flow
 */
export let hasBadMapPolyfill: boolean;
  if (__DEV__) {
   hasBadMapPolyfill = false;
   try {
     const frozenObject = Object.freeze({});
     /* eslint-disable no-new */
     new Map([[frozenObject, null]]);
     new Set([frozenObject]);
     /* eslint-enable no-new */
   } catch (e) {
     // TODO: Consider war...

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