run following command

yarn install
yarn start

and access to following URL

• http://localhost:1234/basic-form/index.html
• http://localhost:1234/basic-hmr/index.html
• http://localhost:1234/basic-routing/index.html
• http://localhost:1234/code-splitting/index.html
• http://localhost:1234/counter/index.html
• http://localhost:1234/real-api/index.html
• http://localhost:1234/socket-hmr/index.html