fix(router): skip router write on duplicate entries

[francoischalifour]

This fixes duplicate entries in the router that happen when router.write is called even though uiState hasn't changed.

Explanation

We used to call the write method of the router at every state change. A state change happens at each UI interaction or whenever a widget is mounted/unmounted. The latter is problematic in component-based flavors of InstantSearch (Vue InstantSearch is the only one relying on InstantSearch 4 right now) because widgets are often added/removed.

The duplicate entry detection check was happening in the history router itself, which meant that whenever users opt-out of this default router and implemented their own, they would get this issue.

This fix checks that router.write needs to be called in the router middleware itself. Since it's one level above the history router, or custom user implementation, it will get fixed no matter the router implementations. We check that the routeState is different from the last received to call router.write. We base the check on routeState, and not uiState, because users might plug their own logic in stateToRoute that returns a routeState that differs from uiState; the two do not necessarily change at the same time.

Related

• fix(router): don't write an existing URL #4392
• Vue Router example sandbox does not work vue-instantsearch#841
• Closes Navigation history is being flooded with duplicate paths vue-instantsearch#839

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 068099c:

Sandbox	Source
InstantSearch.js	Configuration

[eunjae-lee]

Looks good to me except for the little thing in the test.

[Haroenv]

makes sense :)