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Add validation to your Redux reducers
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README.md

Redux Store Validator

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Wrapper to add validation to your Redux reducers

npm install --save redux-store-validator

Purpose

In a large React/Redux app, the store can become intractable. A common cause of bugs is when the data in the store has changed in a way that the developer didn't expect. redux-store-validator is intended to facilitate adding detection of when such a scenario occurs. You can add as many or as little validators to specific parts of your store, and act on it accordingly. For example, you can add a validator to check that a value which you expected to be always positive ever becomes negative. If so, you can log or recover right after the offending action modifies the store.

Usage

Wrap your reducers

reducers/index.js

import { withValidation } from 'redux-store-validator';

import aReducer, { validator as aValidator } from './a';
import { bReducer } from './b';

const reducers = {
  a: aReducer,
  b: bReducer
}

const validators = {
  // Only add validators for substates you want validation on
  a: aValidator
}

// Instead of
// const rootReducer = combineReducers(reducers);
// You wrap your reducers in 'withValidation' and pass in the validators to execute
const rootReducer = combineReducers(withValidation(reducers, validators));

Add validators to reducers as needed

reducers/a.js

export function validator(state) {
  return state.word === 'asdf';
}

export default function(state, action) {
  switch(action.type) {
    case 'asdf':
      state.word = 'asdf';
      return state;
    default:
      return state;
  }
}

That's it. After you've wrapped your reducers and added validators, you can detect if the store has become invalid by querying the state.

redux-store-validator adds the following to your redux state:

state[INVALID_KEYS]: Array of keys which correspond to the substates that are invalid.

You can act upon it however you like. Below are just a few examples

Examples of acting upon invalid store

In your component you can choose not to render with the new data if it's invalid.

components/myComponent.jsx

import { INVALID_KEYS } from 'redux-store-validator';
...

const myComponent = React.createClass({
  props: {
    text: PropTypes.string,
    isValid: PropTypes.bool
  },

  shouldComponentUpdate(nextProps) {
    return nextProps.isValid;
  },

  ...
  
  render() {
    return <div>{this.props.text}</div>;
  }
});

function mapStateToProps(state) {
  return {
    text: state.a.word,
    isValid: state[INVALID_KEYS].includes('a')
  }
}
...

You can replace the state with a default valid one as soon as an action caused it to become invalid.

Back in reducers/index.js

import aReducer, {
  validator as aValidator,
  defaultState as aDefaultState
} from './a';
import { bReducer } from './b';

import { INVALID_KEYS } from 'redux-store-validator';

const reducers = {
  a: aReducer,
  b: bReducer
}

const validators = {
  // Only add validators for substates you want validation on
  a: aValidator
}

const defaultStates = {
  a: aDefaultState
}

const rootReducer = combineReducers(withValidation(reducers, validators));

function replaceInvalid(combinedReducer) {
  return (state, action) => {
    const newState = combinedReducer(state, action);
    if (newState.INVALID_KEYS.length === 0) {
      return newState;
    }
    for (const validatedSubstate of Object.keys(validators)) {
      if (newState[INVALID_KEYS].includes(validatedSubstate)) {
        newState[validatedSubstate] = defaultStates[validatedSubstate]
        // If the default state is valid, the INVALID_KEYS will remove the state key in the next reduction step
      }
    }
    return newState;
  }
}
export default replaceInvalid(rootReducer);

You can log in a logger middleware

middlewares/Logger.js

import { INVALID_KEYS } from 'redux-store-validator';

export default ({getState}) => (next) => (action) => {
  const state = getState(); 
  if (state[INVALID_KEYS].length !== 0) {
    // Log the invalid states
    for (const key of state[INVALID_KEYS]) {
      const substate = state[key];
      ...
    }
    ...
  }
  ...
  return next(action);
}
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