Require action types to be strings

[EskiMojo14]

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name: 🐛 Bug fix or new feature
about: Require action types to be strings

PR Type

Does this PR add a new feature, or fix a bug?

It prevents passing non-string action types to store.

Why should this PR be included?

Per #4129 (comment) :

we've always said they should be serializable, and ought to be strings.

Someone over on Twitter said they'd once tried to use Symbols to make them truly unique, but tbh slice namespacing gives you like 95% uniqueness anyway, so I don't see that as a reason to continue to allow them. As mentioned above, TS enums can have number values, but again why would you do that? We want them to be readable in the DevTools.

So, given that we've always effectively said they should be strings, we might as well enforce it.

Checklist

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Is there an existing issue for this PR?
  • Actually require that action.type must be a string #4543
• Have the files been linted and formatted?
• Have the docs been updated to match the changes in the PR?
• Have the tests been updated to match the changes in the PR?
• Have you run the tests locally to confirm they pass?

Bug Fixes

What is the current behavior, and the steps to reproduce the issue?

Non-string action types are allowed to be dispatched to store.

What is the expected behavior?

Action types should be enforced as string

How does this PR fix the problem?

Store throws an error if action type is not string.

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[markerikson]

Heh, technically the docs update will apply now, but hey, why not :)

[EskiMojo14]

yeah, technically there's no harm in the docs saying that action types must be strings early 😄