Idiomatic way to handle website closed/leave page events with React/React Router

I want to send a cleanup request to my API sever when the user leaves the website (actually closes the tab/browser, not just changes page in the SPA). Is there an idiomatic way to do this in an app using React with React Router? Will componentWillUnmount fire on page close? I assume not.

React doesn't do any special thing here for you. Just do that you usually do for this. Also, see answers to a related question

The best place to put this subscription code is the componentDidMount lifecycle method. And do not forget to unsubscribe it on componentWillUnmount to prevent leaks.