hasBadMapPolyfill

位于 react/src/BadMapPolyfill.js

该属性用来标记 Map 和 Set 对象是否polyfill过。

生产环境下为 undefined, 即 false, 默认认为全局有 Map 和 Set 对象 开发环境下会检测:

export let hasBadMapPolyfill;

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 warning about bad polyfills
    hasBadMapPolyfill = true;
  }
}

可以看到，如果全局对象中没有 Map 或者 Set 对象，try {} 代码块就会报错，进而 hasBadMapPolyfill 就会为 true。

Browser API Access Restrictions

Because VuePress applications are server-rendered in Node.js when generating static builds, any Vue usage must conform to the universal code requirements. In short, make sure to only access Browser / DOM APIs in beforeMount or mounted hooks.

If you are using or demoing components that are not SSR friendly (for example containing custom directives), you can wrap them inside the built-in <ClientOnly> component:

IsSomeRendererActing

位于 react/src/IsSomeRendererActing.js

该对象被 act() 用来追踪当前代码是否在 act() 作用域内执行, 改变量是一个对象，有一个 boolean 类型的 current 属性

// Used by act() to track whether you're inside an act() scope.
const IsSomeRendererActing = {
  current: (false: boolean),
};
export default IsSomeRendererActing;