code: function mapModule(state, module) {
    var moduleMap = state.opts.map || {};
    if (moduleMap.hasOwnProperty(module)) {
      return moduleMap[module];
    }
    // Jest understands the haste module system, so leave modules intact.
    if (process.env.NODE_ENV === 'test') {
      return;
    }
    return './' + path.basename(module);
  }
docs: This file is a fork from fbjs's transform of the same name. It has been
  modified to also apply to import statements, and to account for relative
  file names in require statements.
   
  Rewrites module string literals according to the `map` and `prefix` options.
  This allows other npm packages to be published and used directly without
  being a part of the same build.