Lazy loading is a mode that allows a developer to specify what components of a program should not be loaded into storage by default when a program is started. Modules/components are only loaded as they are specifically requested.
After running the application locally, You can check that a module is being lazy loaded with the Chrome developer tools. In Chrome, open the dev tools by pressing Cmd+Option+i on a Mac or Ctrl+Alt+i on a PC and go to the Network Tab.