Connecting a Redux Store to the View

Once the view layer is up and running, the next step is to mount the view into the application. The view layer will be mounted into a “delta”. A delta is a function that takes a stream of actions$ and a stream of state$ from Redux and returns a new stream of actions that get emitted into the store. This is bound into the store through the observeDelta middleware.

domDelta is implemented as a function that returns a delta, and all userland deltas should be implemented this way. First, define the relevant functions for the delta:

// dom.js
import { Kefir, observeDelta, domDelta, component } from 'brookjs';

const view = component({
    onMount: () => Kefir.constant({ type: 'MOUNT_VIEW' })

export const el = doc => fromCallback(cb => {

export const selectProps = state$ => state$.map(state => ({
    isProps: true

selectProps should be a function that maps a stream of state$ values from the Redux store to a stream of props$ for the dom delta. el should be either an Element or a stream-returning function that emits a single Element then ends. This function will be passed the document so it can be unit tested. view should be the root component, responsible for rendering the entire DOM. These need to be passed into the configuration object for domDelta.

The observeDelta middleware can now be mounted into the store:

import { createStore, applyMiddleware } from 'redux';
import deltaMiddleware from './dom';
import reducer from './reducer';

const deltaMiddleware = observeDelta(
    domDelta({ el, view, selectProps })

export default createStore(reducer, applyMiddleware(deltaMiddleware));

Because the domDelta won’t be mounted until the DOMContentLoaded event has fired or the DOM has fully loaded, providing a stream allows the query process to be deferred until the DOM is ready.