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Throw error on undefined value from store function #193

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Throw error on undefined value from store function #193

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17 changes: 12 additions & 5 deletions src/utils/composeStores.js
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Original file line number Diff line number Diff line change
@@ -1,11 +1,18 @@
import mapValues from '../utils/mapValues';
import pick from '../utils/pick';
import mapValues from './mapValues';
import pick from './pick';

// UNDEF = undefined;
const UNDEF = void 0;
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It looks like a hack. Can you please check typeof instead?

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This is a pretty common pattern. I will make the change. How should I fix the other UNDEF use in the test?

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You can replace return UNDEF with just return, and use typeof x === 'undefined' as a check.
Or are you referring to something else?

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Unfortunately, there is an ESLint rule that forbids return; when there is another type returned elsewhere. I think we can just use undefined though. We don't have to worry about users overwriting undefined in tests.

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I think you can also invert the condition.
Instead of returning undefined in some cases, return something in other cases.

function bad() {
  if (action.type !== 'something') {
    return something;
  }
}

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I thought about that. I was trying to make the test as obvious as possible. I will change it to above


export default function composeStores(stores) {
const finalStores = pick(stores, (val) => typeof val === 'function');
return function Composition(atom = {}, action) {
return mapValues(finalStores, (store, key) =>
store(atom[key], action)
);
return mapValues(finalStores, (store, key) => {
const state = store(atom[key], action);
if (state === UNDEF) {
throw new Error(`Store ${key} returns undefined. By default store should return original state.`);
}
return state;
});
};
}
27 changes: 27 additions & 0 deletions test/composeStores.spec.js
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Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
import expect from 'expect';
import { composeStores } from '../src';

// UNDEF = undefined;
const UNDEF = void 0;

describe('Utils', () => {
describe('composeStores', () => {
it('should return a store that maps state keys to reducer functions', () => {
Expand All @@ -27,5 +30,29 @@ describe('Utils', () => {

expect(Object.keys(store({}, {type: 'push'}))).toEqual(['stack']);
});
it('should throw an error if undefined return from store', () => {
const store = composeStores({
stack: (state = []) => state,
bad: (state = [], action) => {
if (action.type === 'something') {
return state;
}
}
});
expect(() => store({}, {type: '@@testType'})).toThrow();
});
it('should throw an error if undefined return not by default', () => {
const store = composeStores({
stack: (state = []) => state,
bad: (state = 1, action) => {
if (action.type === 'something') {
return UNDEF;
}
return state;
}
});
expect(store({}, {type: '@@testType'})).toEqual({stack: [], bad: 1});
expect(() => store({}, {type: 'something'})).toThrow();
});
});
});