Pending state

[amannn]

Is your feature request related to a problem? Please describe.

It would be very helpful if the user could obtain a flag that indicates if the router is currently transitioning to a new page. This might take some time until gSSP is called again and the data returns, therefore the user should be informed.

Describe the solution you'd like

Some kind of access to a global flag.

Describe alternatives you've considered

Tracking this in user land in separate state.

[amannn]

router.replace returns a promise, probably that's good enough.