knockout-store

State management for Knockout apps. Inspired by Redux and react-redux.

Managing app state is hard. While tools like Redux exist to solve this problem, mixing Redux and Knockout might be overkill for your app. Knockout already has observables which offer some of the functionality provided by a Redux store, namely subscriptions.

knockout-store is a tiny library offering an API for app state management in Knockout apps. Define your app state once using setState, and then connect your view models with the connect method. This enables developers to decouple view models from one another, by giving each view model access to the app state instead.

For a deeper understanding of the library and the motivation behind it, see the wiki.

Installation

The best way to use knockout-store is to add it as an npm dependency.

npm install --save knockout-store

Once installed, knockout-store supports several types of imports.

ES6

import { connect, getState, setState } from 'knockout-store';

UMD Require

const knockoutStore = require('knockout-store');

UMD Script Tag

Referencing a script in the dist directory on a page will add the API methods to ko.store.

<script src="node_modules/knockout-store/dist/knockout-store.js"></script>
<!-- Or... -->
<script src="node_modules/knockout-store/dist/knockout-store.min.js"></script>

Then, in JavaScript:

ko.store.setState(someStateObject);

Usage

Here's a small example, skip to the API section for details on the methods.

Setting the App State

import ko from 'knockout';
import { setState } from 'knockout-store';
 
const state = {
    cats: ko.observableArray(['Mr. Whiskers', 'Charles', 'Missy']),
    selectedCat: ko.observable()
};
 
setState(state);

Connecting a View Model

This might look familiar if you've used react-redux.

import { connect } from 'knockout-store';
 
function CatSelectorViewModel(params) {
    const self = this;
    self.cats = params.cats;    // from the state object, see mapStateToParams below
    self.selectCat = function(cat) {
        params.selectedCat(cat);    // also from the state object
    }
}
 
function mapStateToParams({ cats, selectedCat }) {  // the state object
    return { cats, selectedCat };   // properties on state to add to view model's params
}
 
export default connect(mapStateToParams)(CatSelectorViewModel);

Connecting Another View Model

import { connect } from 'knockout-store';
 
function SelectedCatDisplayViewModel(params) {
    const self = this;
    // Since params.selectedCat is an observable,
    // this computed will update appropriately
    // after selectedCat is updated in the other view model.
    self.selectedCatText = ko.computed(() => `You've selected ${params.selectedCat()}!`));
}
 
function mapStateToParams({ selectedCat }) {
    return { selectedCat };
}
 
export default connect(mapStateToParams)(SelectedCatDisplayViewModel);

Confused? Have a look at the wiki for a more in-depth example.

Using the Connected View Models

connect returns a wrapped view model and can be used like any other view model.

import CatSelectorViewModel from './cat-selector-view-model';
import SelectedCatDisplayViewModel from './selected-cat-display-view-model';
 
ko.applyBindings(CatSelectorViewModel, document.getElementById('cat-selector'));
ko.applyBindings(SelectedCatDisplayViewModel, document.getElementById('selected-cat-display'));

Note: Use with Knockout Components for a more modern development experience. See knockout-store-todo.

API

setState(state)

Sets the app state to have value of state. state is stored in an observable, which you can access through the getState() method (see below). For most cases, state will be an object made up of other observable properties. In this situation, calling setState again will overwrite the object and all subscriptions will be lost. For this reason, it's unlikely this should be called more than once.

Arguments

• state: The object to store in the app state observable.

getState()

Returns the app state observable. If you need to subscribe directly to the app state, you can do so with this method.

const stateObservable = getState();
stateObservable.subscribe((newState) => {
    // do something with the new state
});

It's usually preferable to connect your view models to the state through the connect() method instead (see below).

connect([mapStateToParams], [mergeParams])

Connects a view model to the app state. Pass the view model to be connected to the result of this function.

Arguments

• mapStateToParams(state, [ownParams]): stateParams: If specified, this argument is a function to map from the app state (state) to the stateParams object passed to mergeParams (see below). state will be the value of the observable returned by getState() (see above). If this argument is null or not specified, a function returning an empty object is used instead.
• mergeParams(stateParams, ownParams): params: If specified, this argument is a function responsible for merging stateParams (the result of mapStateToParams, see above) and ownParams (the params object the connected view model was called with). If this argument is null or not specified, Object.assign({}, ownParams, stateParams) is used instead.

Testing

Run npm run test to start the Karma test runner with PhantomJS. You can also run npm run test-with-chrome to test with Google Chrome instead of PhantomJS if that's more your thing. If you just want to run the tests once, you can use npm run test-once.

License

Licensed under the MIT License.