angular/packages/platform-server/init/PACKAGE.md

Initializes the server environment for rendering an Angular application.

For example, it provides shims (such as DOM globals) for the server environment.

The initialization happens as a side effect of importing the entry point (i.e. there are no specific exports):

import '@angular/platform-server/init';

The import must come before any imports (direct or transitive) that rely on DOM built-ins being available.