React Redux Reselect - Undefined State

Question

I have the following code in my react/redux app:

import { createSelector } from 'reselect';

const selectMembers = state => state.membersData;

const makeSelectLessonSets = createSelector(
  selectMembers,
  substate => substate.get('myData').toJS()
);

The problem is that sometimes myData is not yet defined, so substate.get('myData') will not get anything. And since I try to call toJS() on it, it shows the error: undefined is not an object.

But I don't know how to check if substate.get('myData') has returned a valid object inside createSelector before I call toJS() on it.

Can you please help with it.

Daniel Bellmas · Accepted Answer · 2021-06-16 05:51:49Z

2

I added ? before the dot this will not throw an error

import { createSelector } from 'reselect';

const selectMembers = state => state.membersData;

const makeSelectLessonSets = createSelector(
  selectMembers,
  substate => substate?.get('myData')?.toJS()
);

answered Jun 16, 2021 at 5:51

Daniel Bellmas

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1 Comment

HMR Over a year ago

It's called optional chaining

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