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Jeremy Fairbank @elpapapollo / jfairbank Get Started with Redux

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Software is broken. We are here to fix it. Say hi@testdouble.com

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The Wild West of State

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var $el = $('[data-id="42"]'); var currentName = $el.data('name'); $el.data('name', currentName.toUpperCase()); Data in the DOM

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Controller View Model Model Model Model Model View View View View MVC

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View Model Model Model Model Model View Model View Model View Model View Model Model Two-way Data Binding

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The Wild West of State State is everywhere and anyone can change it!

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Predictable State Container

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All application state in one place State Container

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Predictable Old State REDUCER New State

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Predictable Old State REDUCER New State • State changes in one place

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Predictable Old State REDUCER New State • State changes in one place • State changes in well-defined ways

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Predictable Old State REDUCER New State • State changes in one place • State changes in well-defined ways • Changes are serialized

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Reducer View State Actions

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Reducer View State Actions

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Reducer View React, Angular, Vanilla JS, etc. State Actions

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Reducer View State Actions Dispatch

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Reducer View State Actions

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incrementBtn.addEventListener('click', () => { counter.innerText = Number(counter.innerText) + 1; }); decrementBtn.addEventListener('click', () => { counter.innerText = Number(counter.innerText) - 1; });

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let state = 0; function render() { counter.innerText = state; } incrementBtn.addEventListener('click', () => { state += 1; render(); }); decrementBtn.addEventListener('click', () => { state -= 1; render(); });

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let state = 0; function render() { counter.innerText = state; } incrementBtn.addEventListener('click', () => { state += 1; render(); }); decrementBtn.addEventListener('click', () => { state -= 1; render(); });

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let state = 0; function render() { counter.innerText = state; } incrementBtn.addEventListener('click', () => { state += 1; render(); }); decrementBtn.addEventListener('click', () => { state -= 1; render(); });

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let state = 0; function render() { counter.innerText = state; } incrementBtn.addEventListener('click', () => { state += 1; render(); }); decrementBtn.addEventListener('click', () => { state -= 1; render(); });

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state += 1; state -= 1; Anyone can access and mutate state

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state += 1 state -= 1 { type: 'INCREMENT' } { type: 'DECREMENT' } Tokens/descriptors that describe a type of change. Actions

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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function reducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } } Returns new state from current state and action. Reducer

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Updating state is just a function call now let state = 0; state = reducer(state, { type: 'INCREMENT' }); // 1 state = reducer(state, { type: 'INCREMENT' }); // 2 state = reducer(state, { type: 'DECREMENT' }); // 1 state = reducer(state, { type: 'ADD_2' }); // 1 console.log(state); // 1

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Updating state is just a function call now let state = 0; state = reducer(state, { type: 'INCREMENT' }); // 1 state = reducer(state, { type: 'INCREMENT' }); // 2 state = reducer(state, { type: 'DECREMENT' }); // 1 state = reducer(state, { type: 'ADD_2' }); // 1 console.log(state); // 1 Unhandled types are ignored

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function dispatch(action) { state = reducer(state, action); render(); } incrementBtn.addEventListener('click', () => { dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { dispatch({ type: 'DECREMENT' }); }); Decouple event from state change.

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function dispatch(action) { state = reducer(state, action); render(); } incrementBtn.addEventListener('click', () => { dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { dispatch({ type: 'DECREMENT' }); }); Decouple event from state change.

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function dispatch(action) { state = reducer(state, action); render(); } incrementBtn.addEventListener('click', () => { dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { dispatch({ type: 'DECREMENT' }); }); Decouple event from state change.

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function dispatch(action) { state = reducer(state, action); render(); } incrementBtn.addEventListener('click', () => { dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { dispatch({ type: 'DECREMENT' }); }); Decouple event from state change.

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function dispatch(action) { state = reducer(state, action); render(); } incrementBtn.addEventListener('click', () => { dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { dispatch({ type: 'DECREMENT' }); }); Decouple event from state change.

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STORE

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import { createStore } from 'redux'; const store = createStore(reducer, 0); store.getState(); // 0

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import { createStore } from 'redux'; const store = createStore(reducer, 0); store.getState(); // 0

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import { createStore } from 'redux'; const store = createStore(reducer, 0); store.getState(); // 0

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import { createStore } from 'redux'; const store = createStore(reducer, 0); store.getState(); // 0

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import { createStore } from 'redux'; const store = createStore(reducer, 0); store.getState(); // 0

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incrementBtn.addEventListener('click', () => { store.dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { store.dispatch({ type: 'DECREMENT' }); }); store.subscribe(() => { counter.innerText = store.getState(); });

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incrementBtn.addEventListener('click', () => { store.dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { store.dispatch({ type: 'DECREMENT' }); }); store.subscribe(() => { counter.innerText = store.getState(); });

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incrementBtn.addEventListener('click', () => { store.dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { store.dispatch({ type: 'DECREMENT' }); }); store.subscribe(() => { counter.innerText = store.getState(); });

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Store Reducer State View 0

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Store Reducer State View 0

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Store Reducer State View 0 getState

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Store Reducer View State 0

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Store Reducer View State 0 INCREMENT dispatch

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Store Reducer View State 0 INCREMENT dispatch

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Store Reducer View State 0

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Store Reducer View State 1

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Store Reducer View State 1

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Store Reducer View State 1 1 subscribe getState

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incrementBtn.addEventListener('click', () => { store.dispatch({ type: 'INCREMENT' }); }); decrementBtn.addEventListener('click', () => { store.dispatch({ type: 'DECREMENT' }); }); Problems: • Creating actions are cumbersome • Requires direct access to store

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const increment = () => ({ type: 'INCREMENT', }); const decrement = () => ({ type: 'DECREMENT', }); Reusable functions that create actions Action Creators

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const increment = () => ({ type: 'INCREMENT', }); const decrement = () => ({ type: 'DECREMENT', }); Reusable functions that create actions Action Creators

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const increment = () => ({ type: 'INCREMENT', }); const decrement = () => ({ type: 'DECREMENT', }); Reusable functions that create actions Action Creators

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incrementBtn.addEventListener('click', () => { store.dispatch(increment()); }); decrementBtn.addEventListener('click', () => { store.dispatch(decrement()); }); Problems: • Creating actions are cumbersome • Requires direct access to store

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const actions = { increment: () => store.dispatch(increment()), decrement: () => store.dispatch(decrement()), }; Automatically dispatch when invoked Bound Action Creators

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const actions = { increment: () => store.dispatch(increment()), decrement: () => store.dispatch(decrement()), }; Automatically dispatch when invoked Bound Action Creators Manually created

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const actions = { increment: () => store.dispatch(increment()), decrement: () => store.dispatch(decrement()), }; Automatically dispatch when invoked Bound Action Creators

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import { bindActionCreators } from 'redux'; const actions = bindActionCreators( { increment, decrement }, store.dispatch ); Automatically dispatch when invoked Bound Action Creators

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import { bindActionCreators } from 'redux'; const actions = bindActionCreators( { increment, decrement }, store.dispatch ); Automatically dispatch when invoked Bound Action Creators

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import { bindActionCreators } from 'redux'; const actions = bindActionCreators( { increment, decrement }, store.dispatch ); Automatically dispatch when invoked Bound Action Creators Automatically created

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Problems: • Creating actions are cumbersome • Requires direct access to store incrementBtn.addEventListener('click', actions.increment); decrementBtn.addEventListener('click', actions.decrement);

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React +

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github.com/reactjs/react-redux npm install --save react-redux Official React bindings for Redux React Redux Library

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Reducer State Actions React Redux

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React Redux React Application

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React Redux React Application Provider

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Component React Redux React Application Provider connect State Action Creators

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Component Child React Redux React Application Provider connect State Child Action Creators

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const MyApp = () => (
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import React from 'react'; import { render } from 'react-dom'; import { Provider } from 'react-redux'; render(( ), document.getElementById('main'));

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import React from 'react'; import { render } from 'react-dom'; import { Provider } from 'react-redux'; render(( ), document.getElementById('main'));

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import React from 'react'; import { render } from 'react-dom'; import { Provider } from 'react-redux'; render(( ), document.getElementById('main'));

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import { connect } from 'react-redux'; const mapStateToProps = counter => ({ counter }); function mapDispatchToProps(dispatch) { return bindActionCreators({ onIncrement: increment, onDecrement: decrement, }, dispatch); } const MyAppContainer = connect( mapStateToProps, mapDispatchToProps )(MyApp);

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import { connect } from 'react-redux'; const mapStateToProps = counter => ({ counter }); function mapDispatchToProps(dispatch) { return bindActionCreators({ onIncrement: increment, onDecrement: decrement, }, dispatch); } const MyAppContainer = connect( mapStateToProps, mapDispatchToProps )(MyApp);

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import { connect } from 'react-redux'; const mapStateToProps = counter => ({ counter }); function mapDispatchToProps(dispatch) { return bindActionCreators({ onIncrement: increment, onDecrement: decrement, }, dispatch); } const MyAppContainer = connect( mapStateToProps, mapDispatchToProps )(MyApp);

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import { connect } from 'react-redux'; const mapStateToProps = counter => ({ counter }); function mapDispatchToProps(dispatch) { return bindActionCreators({ onIncrement: increment, onDecrement: decrement, }, dispatch); } const MyAppContainer = connect( mapStateToProps, mapDispatchToProps )(MyApp);

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import { connect } from 'react-redux'; const mapStateToProps = counter => ({ counter }); function mapDispatchToProps(dispatch) { return bindActionCreators({ onIncrement: increment, onDecrement: decrement, }, dispatch); } const MyAppContainer = connect( mapStateToProps, mapDispatchToProps )(MyApp);

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const MyApp = (props) => (
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const MyApp = (props) => (
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const MyApp = (props) => (
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Immutable Object State

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const initialState = { counter: 0, car: { color: 'red', }, };

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const initialState = { counter: 0, car: { color: 'red', }, };

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const initialState = { counter: 0, car: { color: 'red', }, };

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const increment = () => ({ type: 'INCREMENT', }); const decrement = () => ({ type: 'DECREMENT', }); const changeColor = color => ({ type: 'CHANGE_COLOR', payload: color, });

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const increment = () => ({ type: 'INCREMENT', }); const decrement = () => ({ type: 'DECREMENT', }); const changeColor = color => ({ type: 'CHANGE_COLOR', payload: color, });

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const increment = () => ({ type: 'INCREMENT', }); const decrement = () => ({ type: 'DECREMENT', }); const changeColor = color => ({ type: 'CHANGE_COLOR', payload: color, });

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function reducer(state = initialState, action) { switch (action.type) { case 'INCREMENT': return { ...state, counter: state.counter + 1 }; case 'DECREMENT': return { ...state, counter: state.counter - 1 }; case 'CHANGE_COLOR': return { ...state, car: { color: action.payload } }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'INCREMENT': return { ...state, counter: state.counter + 1 }; case 'DECREMENT': return { ...state, counter: state.counter - 1 }; case 'CHANGE_COLOR': return { ...state, car: { color: action.payload } }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'INCREMENT': return { ...state, counter: state.counter + 1 }; case 'DECREMENT': return { ...state, counter: state.counter - 1 }; case 'CHANGE_COLOR': return { ...state, car: { color: action.payload } }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'INCREMENT': return { ...state, counter: state.counter + 1 }; case 'DECREMENT': return { ...state, counter: state.counter - 1 }; case 'CHANGE_COLOR': return { ...state, car: { color: action.payload } }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'INCREMENT': return { ...state, counter: state.counter + 1 }; case 'DECREMENT': return { ...state, counter: state.counter - 1 }; case 'CHANGE_COLOR': return { ...state, car: { color: action.payload } }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'INCREMENT': return { ...state, counter: state.counter + 1 }; case 'DECREMENT': return { ...state, counter: state.counter - 1 }; case 'CHANGE_COLOR': return { ...state, car: { color: action.payload } }; default: return state; } }

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store.subscribe(() => { console.log('state =', store.getState()); }); store.dispatch(increment()); store.dispatch(changeColor('green')); // state = { counter: 1, car: { color: 'red' } } // state = { counter: 1, car: { color: 'green' } }

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store.subscribe(() => { console.log('state =', store.getState()); }); store.dispatch(increment()); store.dispatch(changeColor('green')); // state = { counter: 1, car: { color: 'red' } } // state = { counter: 1, car: { color: 'green' } }

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store.subscribe(() => { console.log('state =', store.getState()); }); store.dispatch(increment()); store.dispatch(changeColor('green')); // state = { counter: 1, car: { color: 'red' } } // state = { counter: 1, car: { color: 'green' } }

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function reducer(state = initialState, action) { }

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Reducer Composition Create modular reducers for better organization and readability

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Root Reducer Counter Reducer Car Reducer

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function counterReducer(state = 0, action) { switch (action.type) { case 'INCREMENT': return state + 1; case 'DECREMENT': return state - 1; default: return state; } }

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const initialState = { color: 'red' }; function carReducer(state = initialState, action) { switch (action.type) { case 'CHANGE_COLOR': return { ...state, color: action.payload }; default: return state; } }

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const initialState = { color: 'red' }; function carReducer(state = initialState, action) { switch (action.type) { case 'CHANGE_COLOR': return { ...state, color: action.payload }; default: return state; } }

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const initialState = { color: 'red' }; function carReducer(state = initialState, action) { switch (action.type) { case 'CHANGE_COLOR': return { ...state, color: action.payload }; default: return state; } }

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function reducer(state = {}, action) { return { counter: counterReducer(state.counter, action), car: carReducer(state.car, action), }; }

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function reducer(state = {}, action) { return { counter: counterReducer(state.counter, action), car: carReducer(state.car, action), }; }

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function reducer(state = {}, action) { return { counter: counterReducer(state.counter, action), car: carReducer(state.car, action), }; }

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function reducer(state = {}, action) { return { counter: counterReducer(state.counter, action), car: carReducer(state.car, action), }; }

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import { combineReducers } from 'redux'; const reducer = combineReducers({ counter: counterReducer, car: carReducer, });

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import { combineReducers } from 'redux'; const reducer = combineReducers({ counter: counterReducer, car: carReducer, });

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import { combineReducers } from 'redux'; const reducer = combineReducers({ counter: counterReducer, car: carReducer, });

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Root Reducer Counter Reducer Car Reducer Engine Reducer Tire Reducer … … …

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Root Reducer Counter Reducer Car Reducer Engine Reducer Tire Reducer … … …

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Root Reducer Counter Reducer Car Reducer Engine Reducer Tire Reducer … … …

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Interact with APIs?

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Middleware Enhance Redux applications

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• Logging Middleware Enhance Redux applications

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• Logging • Debugging Middleware Enhance Redux applications

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• Logging • Debugging • API interaction Middleware Enhance Redux applications

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• Logging • Debugging • API interaction • Custom actions Middleware Enhance Redux applications

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Reducer View State Actions Middleware

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Reducer View State Actions Middleware Intercept

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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const logMiddleware = api => next => action => { console.log('dispatch', action); const result = next(action); console.log('state =', api.getState()); return result; };

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import { applyMiddleware } from 'redux'; const store = createStore( reducer, applyMiddleware(logMiddleware) ); store.dispatch(increment()); store.dispatch(changeColor('green')); // dispatch { type: 'INCREMENT' } // state = { counter: 1, car: { color: 'red' } } // dispatch { type: 'CHANGE_COLOR', payload: 'green' } // state = { counter: 1, car: { color: 'green' } }

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import { applyMiddleware } from 'redux'; const store = createStore( reducer, applyMiddleware(logMiddleware) ); store.dispatch(increment()); store.dispatch(changeColor('green')); // dispatch { type: 'INCREMENT' } // state = { counter: 1, car: { color: 'red' } } // dispatch { type: 'CHANGE_COLOR', payload: 'green' } // state = { counter: 1, car: { color: 'green' } }

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import { applyMiddleware } from 'redux'; const store = createStore( reducer, applyMiddleware(logMiddleware) ); store.dispatch(increment()); store.dispatch(changeColor('green')); // dispatch { type: 'INCREMENT' } // state = { counter: 1, car: { color: 'red' } } // dispatch { type: 'CHANGE_COLOR', payload: 'green' } // state = { counter: 1, car: { color: 'green' } }

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import { applyMiddleware } from 'redux'; const store = createStore( reducer, applyMiddleware(logMiddleware) ); store.dispatch(increment()); store.dispatch(changeColor('green')); // dispatch { type: 'INCREMENT' } // state = { counter: 1, car: { color: 'red' } } // dispatch { type: 'CHANGE_COLOR', payload: 'green' } // state = { counter: 1, car: { color: 'green' } }

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import { applyMiddleware } from 'redux'; const store = createStore( reducer, applyMiddleware(logMiddleware) ); store.dispatch(increment()); store.dispatch(changeColor('green')); // dispatch { type: 'INCREMENT' } // state = { counter: 1, car: { color: 'red' } } // dispatch { type: 'CHANGE_COLOR', payload: 'green' } // state = { counter: 1, car: { color: 'green' } }

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const initialState = { status: 'READY', user: null, };

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function reducer(state = initialState, action) { switch (action.type) { case 'REQUEST_USER': return { ...state, status: 'FETCHING' }; case 'RECEIVE_USER': return { ...state, status: 'SUCCESS', user: action.payload, }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'REQUEST_USER': return { ...state, status: 'FETCHING' }; case 'RECEIVE_USER': return { ...state, status: 'SUCCESS', user: action.payload, }; default: return state; } }

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function reducer(state = initialState, action) { switch (action.type) { case 'REQUEST_USER': return { ...state, status: 'FETCHING' }; case 'RECEIVE_USER': return { ...state, status: 'SUCCESS', user: action.payload, }; default: return state; } }

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const requestUser = id => ({ type: 'REQUEST_USER', payload: id, }); const receiveUser = user => ({ type: 'RECEIVE_USER', payload: user, });

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const store = createStore(reducer); function fetchUser(id) { store.dispatch(requestUser(id)); axios.get(`/users/${id}`) .then(({ data: user }) => { store.dispatch(receiveUser(user)); }); } fetchUser(1);

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const store = createStore(reducer); function fetchUser(id) { store.dispatch(requestUser(id)); axios.get(`/users/${id}`) .then(({ data: user }) => { store.dispatch(receiveUser(user)); }); } fetchUser(1);

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const store = createStore(reducer); function fetchUser(id) { store.dispatch(requestUser(id)); axios.get(`/users/${id}`) .then(({ data: user }) => { store.dispatch(receiveUser(user)); }); } fetchUser(1);

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const thunkMiddleware = api => next => action => { if (typeof action === 'function') { return action(api.dispatch); } return next(action); }; const store = createStore( reducer, applyMiddleware(thunkMiddleware) );

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const thunkMiddleware = api => next => action => { if (typeof action === 'function') { return action(api.dispatch); } return next(action); }; const store = createStore( reducer, applyMiddleware(thunkMiddleware) );

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const thunkMiddleware = api => next => action => { if (typeof action === 'function') { return action(api.dispatch); } return next(action); }; const store = createStore( reducer, applyMiddleware(thunkMiddleware) );

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const thunkMiddleware = api => next => action => { if (typeof action === 'function') { return action(api.dispatch); } return next(action); }; const store = createStore( reducer, applyMiddleware(thunkMiddleware) );

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function fetchUser(id) { return dispatch => { dispatch(requestUser(id)); return axios.get(`/users/${id}`) .then(({ data: user }) => { dispatch(receiveUser(user)); }); }; } store.dispatch(fetchUser(1));

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function fetchUser(id) { return dispatch => { dispatch(requestUser(id)); return axios.get(`/users/${id}`) .then(({ data: user }) => { dispatch(receiveUser(user)); }); }; } store.dispatch(fetchUser(1)); Action Creator

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function fetchUser(id) { return dispatch => { dispatch(requestUser(id)); return axios.get(`/users/${id}`) .then(({ data: user }) => { dispatch(receiveUser(user)); }); }; } store.dispatch(fetchUser(1)); Action

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function fetchUser(id) { return dispatch => { dispatch(requestUser(id)); return axios.get(`/users/${id}`) .then(({ data: user }) => { dispatch(receiveUser(user)); }); }; } store.dispatch(fetchUser(1));

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Alternative Async Middleware

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redux-saga.js.org

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• Uses ES6 generator functions redux-saga.js.org

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• Uses ES6 generator functions • Write asynchronous code in synchronous manner redux-saga.js.org

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• Uses ES6 generator functions • Write asynchronous code in synchronous manner • Great for coordinating multiple API calls redux-saga.js.org

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• Uses ES6 generator functions • Write asynchronous code in synchronous manner • Great for coordinating multiple API calls • Great for forking background tasks redux-saga.js.org

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redux-observable.js.org

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redux-observable.js.org • Uses RxJS observables

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redux-observable.js.org • Uses RxJS observables • Write asynchronous code with declarative observable chains

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redux-observable.js.org • Uses RxJS observables • Write asynchronous code with declarative observable chains • Great for composing asynchronous operations

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redux-observable.js.org • Uses RxJS observables • Write asynchronous code with declarative observable chains • Great for composing asynchronous operations • Very concise code

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And plenty more options…

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• redux-logic And plenty more options…

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• redux-logic • redux-ship And plenty more options…

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• redux-logic • redux-ship • redux-promise And plenty more options…

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• redux-logic • redux-ship • redux-promise • redux-api-middleware And plenty more options…

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× ✓ Testing

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const state = { counter: 0, car: { color: 'red' }, }; it('returns initial state', () => { expect(reducer(undefined, {})).toEqual(state); }); it('increments the number', () => { const subject = reducer(state, increment()).counter; expect(subject).toBe(1); }); it('changes the car color', () => { const subject = reducer(state, changeColor('green')).car.color; expect(subject).toBe('green'); }); Easy reducer unit tests!

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it('creates an INCREMENT action', () => { expect(increment()).toEqual({ type: 'INCREMENT' }); }); it('creates a CHANGE_COLOR action', () => { expect(changeColor('blue')).toEqual({ type: 'CHANGE_COLOR', payload: 'blue', }); }); You can test action creators, but not really necessary.

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However, you should test async action creators. function fetchUser(id) { return dispatch => { dispatch(requestUser(id)); return axios.get(`/users/${id}`) .then(({ data: user }) => { dispatch(receiveUser(user)); }); }; }

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); }); Unit test with test doubles

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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import td from 'testdouble'; const axios = td.replace('axios'); it('fetches a user', () => { // Arrange const dispatch = td.function(); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act return fetchUser(1)(dispatch).then(() => { const subject = td.matchers.captor(); td.verify(dispatch(subject.capture())); // Assert expect(subject.values[0]).toEqual(requestUser(1)); expect(subject.values[1]).toEqual(receiveUser('fake user’)); }); });

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Use integration tests to ensure all pieces work together. Allow store, reducer, and actions to all interact .

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it('fetches a user', () => { // Arrange const store = createStore(reducer, applyMiddleware(thunkMiddleware)); td.replace(axios, 'get'); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act const promise = store.dispatch(fetchUser(1)); const subject = store.getState; // Assert expect(subject()).toEqual({ status: 'FETCHING', user: null }); return promise.then(() => { expect(subject()).toEqual({ status: 'SUCCESS', user: 'fake user' }); }); });

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it('fetches a user', () => { // Arrange const store = createStore(reducer, applyMiddleware(thunkMiddleware)); td.replace(axios, 'get'); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act const promise = store.dispatch(fetchUser(1)); const subject = store.getState; // Assert expect(subject()).toEqual({ status: 'FETCHING', user: null }); return promise.then(() => { expect(subject()).toEqual({ status: 'SUCCESS', user: 'fake user' }); }); });

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it('fetches a user', () => { // Arrange const store = createStore(reducer, applyMiddleware(thunkMiddleware)); td.replace(axios, 'get'); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act const promise = store.dispatch(fetchUser(1)); const subject = store.getState; // Assert expect(subject()).toEqual({ status: 'FETCHING', user: null }); return promise.then(() => { expect(subject()).toEqual({ status: 'SUCCESS', user: 'fake user' }); }); });

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it('fetches a user', () => { // Arrange const store = createStore(reducer, applyMiddleware(thunkMiddleware)); td.replace(axios, 'get'); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act const promise = store.dispatch(fetchUser(1)); const subject = store.getState; // Assert expect(subject()).toEqual({ status: 'FETCHING', user: null }); return promise.then(() => { expect(subject()).toEqual({ status: 'SUCCESS', user: 'fake user' }); }); });

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it('fetches a user', () => { // Arrange const store = createStore(reducer, applyMiddleware(thunkMiddleware)); td.replace(axios, 'get'); td.when(axios.get('/users/1')).thenResolve({ data: 'fake user' }); // Act const promise = store.dispatch(fetchUser(1)); const subject = store.getState; // Assert expect(subject()).toEqual({ status: 'FETCHING', user: null }); return promise.then(() => { expect(subject()).toEqual({ status: 'SUCCESS', user: 'fake user' }); }); });

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Resources • Redux • redux.js.org • egghead.io/courses/getting-started-with- redux • React • github.com/reactjs/react-redux

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Thanks! Slides: bit.ly/redux-connect Jeremy Fairbank @elpapapollo / jfairbank