How do I see all the member methods and properties of an external library like a node module?

Where would you like to see them? Is it about code completion, or?

Yes code completion, like typing in "GoogleMapReact." and seeing a list of methods and properties. But I'm open to all the other ways of seeing them in webstorm that I didn't think of.

installing typings (using npm install @types/google-map-react, or via the intention available on Alt+Enter - see https://www.jetbrains.com/help/webstorm/configuring-javascript-libraries.html#ws_jsconfigure_libraries_ts_definition_files) should help:

Thank you so much Elena