Jannes V Jannes V - 1 year ago 182
React JSX Question

Cannot dispatch in the middle of a dispatch

So the error I get is:

Uncaught (in promise) Error: Invariant Violation: Dispatch.dispatch(...): Cannot dispatch in the middle of a dispatch.(…)

I've read through countless of posts regarding this error but I can't seem to figure out why I get it. I get the error at pageload, from thereon it works fine. When I remove the loading action:
loading: StudentsActions.studentsLoading
it all works fine.

You can find all the code on the github repo

Thanks in advance !

Answer Source

You are getting this error because you perform multiple dispatches at the same time. When the page loads, your NavBar component and your StudentList component are both rendered, which invokes componentDidMount on both, and in your case you initiate a dispatch in both places.

You are using a bad flux pattern by having "presentation" components interact with your dispatcher/stores. The correct approach, as pointed out in the flux documentation, is to have a single, top-level component handle dispatches and pass down state to other components via props. In your case, the App component is the only one that should be aware of the stores or that can dispatch actions.

This has many advantages, such as making your entire application far easier to use and refactor since most components don't know or care where the data comes from. It will also prevent the error you're getting. The reason flux does not allow multiple dispatches at the same time is because allowing it would lead to situations where it's unclear why your application is in a particular state. There is no longer a single line of logic that can be followed to determine what your application is doing.

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