feat(store): action status "PreHandler"

[XavierDupessey]

Before this change, it was not possible to prepare for an action before it was processed by NGXS.

This is because the DISPATCHED event is emitted only after the action handlers have been executed, which is unclear from the documentation: ofActionDispatched: This will ONLY grab actions that have just been dispatched

Since changing this behavior would break the public API, this update introduces a new event, PreHandler, which allows reacting to an action before any handler is executed.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngxs/store/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Doc will be adapted if the PR is accepted (page to update is https://www.ngxs.io/concepts/actions/action-handlers)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Currently, it was not possible to prepare for an action before it was processed by NGXS.

What is the new behavior?

The action PreHandler is emitted before NGXS executes any handler.

Does this PR introduce a breaking change?

[ ] Yes
[x] No (except if triggering more ofAction(MyAction) is a breaking change?

[XavierDupessey]

FYI @markwhitfeld this is the new feature I mentioned earlier :)

[nx-cloud]

View your CI Pipeline Execution ↗ for commit af4af0e.

Command	Status	Duration	Result
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☁️ Nx Cloud last updated this comment at 2025-02-17 16:32:51 UTC

[codeclimate]

Code Climate has analyzed commit af4af0e and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 95.3% (0.0% change).

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[markwhitfeld]

Hi @XavierDupessey
Have you thought about implementing this callback through a dedicated plugin?
The Plugin API allows you to intercept each action call before it calls the handlers.
This plugin could expose a BeforeDispatch stream that is similar to the Actions stream.

[XavierDupessey]

No, I hadn't considered implementing it as a plugin first. But you're right, it's very straightforward using the handle function provided by NgxsPlugin from @ngxs/store/plugins.

If you believe there's no need to expose this event in the core, I'm totally fine with going the plugin route instead! 🙂

[markwhitfeld]

I'll have a chat with the team about it, but for now I think that the plugin route is best.
If you would like to contribute a page to our "Recipes" section of the docs with the code that you create and some instructions, that would be a great way to share the pattern with the community.