04. Client Router/02. Pending UI (💪 problem)

Pending UI

👨‍💼 Sometimes our users are on slow networks so we should give them good feedback when they interact with our application.

To be able to do this effectively, we need a few things:

Our transitions should take place within a useTransition startTransition
The location to remain unchanged until the transition is complete
We need a nextLocation state so we can determine what part of the location is changing

We've already got our transition wrapped in a startTransition, but this is the global one from react. We need to use one from useTransition instead so we get access to the isPending state.

Then we'll change our location to be a nextLocation and then use useDeferredValue to get the location so that it remains unchanged until the transition is complete.

Then we can add the isPending and nextLocation to our router context and use that to determine pending states for our UI.

🧝‍♂️ You're going to want to use the parseLocationState utility I made for this one. Here's how it works:

import { parseLocationState } from './router.js'

const location = '/abc123?search=starship'
const state = parseLocationState(location)
// ^ { shipId: 'abc123', search: 'starship' }

You can use that to parse the current location and the next location. If the part you care about is different then you know you can show a pending state.

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