Material-ui can directly introduce the entire library, but sometimes only the required components, such as AppBar, are introduced in order to reduce the size of js.

import AppBar from 'material-ui/AppBar';

In this way, only the AppBar component will be introduced, and the entire material-ui will not be introduced, thus reducing the size of the packaged js.
My question ismaininpackage.jsonspecifies the entry file for each package. In this case, how is the introduction of a single component implemented, that is,material -How is the bar in ui/AppBarimplemented?