🐞[BUG]: Uncaught TypeError: Cannot read properties of undefined (reading 'SystemState') about store

[qq253498229]

I tried changing it to this syntax, and the application can execute properly:

  static list() {
    return createSelector([CronState, SystemState], ({cronMap}: CronStateModel, {currentTime}: SystemStateModel) => {
      console.log('list', cronMap, currentTime);
      return [];
    });
  }

[arturovt]

This is a circular reference issue: system.state.ts -> cron/index.ts -> cron.selector.ts -> system/index.ts -> system.state.ts. Consider updating your file structure and remove barrel files where they're redundant.

[qq253498229]

Oh my goodness!

I used to encounter similar errors frequently before, and every time, I didn't know why they were happening or why they were resolved after fixing them.

Your answer helped me a lot.

[qq253498229]

@arturovt May I ask if you have any suggestions regarding the 'barrel file'? I'm not sure whether I should delete it completely, as it does seem quite useful.

[arturovt]

Barrel files are used to simplify imports for external consumers, but they're always leading to circular references if not managed carefully. It's likely always a circular reference when you face an error stating 'cannot read properties of undefined, reading some class'. You either have to import the file directly from the chain (not cron, but cron/actions), because those files are neighbors, located in 2 close folders. Or you can do a dependency inversion, i.e., dispatch ResetConfig outside the system state through actions$.pipe(ofActionSuccessfull(SystemAction.ResetConfig)).subscribe(() => store.dispatch(new ResetConfig())).

[qq253498229]

Following your advice, I changed the references to 'cron.action' in 'system.state' to 'directly file,' and the application is running fine.

However, when I tried a different way by modifying the import of 'system.state' in 'cron.selector,' it cause an error.

Why is that?

Uncaught ReferenceError: Cannot access 'SystemState' before initialization

[qq253498229]

I've deleted all index.ts files, and now the world is filled with peace and love.