redux-state-change-listener

A simple library for redux for listening on changes of a specific part of redux state tree.

Purpose

Redux started as a library to be used with React but quickly became an independent library that has a very good bindings with React. When using redux with something other than react, the ease provided by mapStateToProps are not available and using the subscribe method itself doesn't seem straight forward. This library provides a very simple binding for listening on changes on the individual items on the redux state tree.

Installation

With npm

npm install --save redux-state-change-listener

With yarn

yarn add redux-state-change-listener

Usage

A callback can be registered to be triggered whenever a specific value on a state tree changes. Consider the following example.

const { createStore } = require('redux');
const ReduxStateChangeListener = require('redux-state-change-listener');

const store = createStore(rootReducer);

// Event called back whenever the todos list is changed
onTodosChanged = (todos, state) => {
  console.log('New set of todos', todos);
}

// Event called back whenever the filter is changed
onFilterChanged = (filter, state, oldFilter, oldState) => {
  console.log(`Todo visibility filter changed from ${oldFilter} to ${filter}`);
}

// Create the state callback manager
const stateCallbackManager = new ReduxStateChangeListener(store);
stateCallbackManager.register(state => state.todos, onTodosChanged);
stateCallbackManager.register(state => state.filter, onFilterChanged);

// Start the manager, after which the callbacks would be called whenever
// the state changes as per the registered event
stateManager.start();

By default, when the value changes to null, it is not considered as a change and the callback is not fired. This could be overriden by passing a third parameter ignoreNull as false. Ex:

stateCallbackManager.register(state => state.todos, onTodosChanged, false);

Advanced Usage

For some advanced use case, you can even check between different values from the current state and the previous state. For this to work, the fourth parameter on register call fireOnTrue should be true. The first parameter in this case must be a function that returns true if the callback needs to be fired. Example:

stateCallbackManager.register((state, prev) => (
  (state.filter === 'ALL' || state.filter === 'INCOMPLETE') && state.todos !== prev.todos
), onActiveTodosChanged, true, true);

NOTE: when the fireOnTrue flag is set, the callback is called with the current state and the previous state as the first and second parameters respectively.

LICENSE

MIT License

Copyright (c) 2017 SharingApples.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.