react-hot-loader/root.js

if (module.hot) {
  var hot = require('./index').hot;
  var cache = require.cache;

  if (!module.parents || module.parents.length === 0) {
    throw new Error(
      'React-Hot-Loader: `react-hot-loader/root` is not supported on your system. ' +
        'Please use `import {hot} from "react-hot-loader"` instead'
    );
  }
  // access parent
  var parent = cache[module.parents[0]];
  if (!parent) {
    throw new Error(
      'React-Hot-Loader: `react-hot-loader/root` is not supported on your system. ' +
        'Please use `import {hot} from "react-hot-loader"` instead'
    );
  }
  // remove self from a cache
  delete cache[module.id];
  // setup hot for caller
  exports.hot = hot(parent);
} else {
  // prod mode
  exports.hot = function(a) {
    return a;
  };
}