fix(useStorage): cross-document sync solution for custom storage backends

[Promise2679]

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Warning: Slowing down new functions

As the VueUse audience continues to grow, we have been inundated with an overwhelming number of feature requests and pull requests. As a result, maintaining the project has become increasingly challenging and has stretched our capacity to its limits. As such, in the near future, we may need to slow down our acceptance of new features and prioritize the stability and quality of existing functions. Please note that new features for VueUse may not be accepted at this time. If you have any new ideas, we suggest that you first incorporate them into your own codebase, iterate on them to suit your needs, and assess their generalizability. If you strongly believe that your ideas are beneficial to the community, you may submit a pull request along with your use cases, and we would be happy to review and discuss them. Thank you for your understanding.

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Description

When using custom storage backends, state changes cannot be synchronized across different documents.

Here is a simple example. If you open two tabs and click the button in tab A, tab B will not update the value instantly.

As mentioned in notes, I solved this by using a BroadcastChannel object to send and receive data.

Additional context

[9romise]

I think the content added in this PR goes outside the responsibility of useStorage.
We also provide useBroadcastChannel, so your use case can be achieved by using useStorage and useBroadcastChannel together.

[Promise2679]

I think the content added in this PR goes outside the responsibility of useStorage. We also provide useBroadcastChannel, so your use case can be achieved by using useStorage and useBroadcastChannel together.

I think since useStorage supports cross-document sync for localStorage (although it is handled by the browser), it should also offer the same capability when using customStorage, rather than a more complicated approach just because a custom storage is used.

Anyway, I am just following the TODO's instruction, I'll respect your final decision.

[9romise]

Anyway, I am just following the TODO's instruction, I'll respect your final decision.

Oh, I see. In this case, would it be possible to use useBroadcastChannel directly instead of implementing it manually?

[Promise2679]

yeah I'll have a try

[Promise2679]

useBroadcastChannel internally listens to the message event, but it doesn't offer a custom callback, so I use a watcher to call the update function.

I'm wondering whether it would make sense to add an onMessage option to useBroadcastChannel.