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OFF THE HOOK REFACTORING S

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YOU MIGHT HAVE HEARD OF REACT https://evilmartians.com/chronicles/optimizing-react-virtual-dom-explained

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1. DECLARATIVE, 2. COMPONENT-BASED, 3. LEARN ONCE, WRITE EVERYWHERE react docs A JAVASCRIPT LIBRARY FOR BUILDING USER INTERFACES

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react docs A JAVASCRIPT LIBRARY FOR BUILDING USER INTERFACES 1. DECLARATIVE, 2. COMPONENT-BASED, 3. LEARN ONCE, WRITE EVERYWHERE

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STATE PROPS https://thenounproject.com/indygo/collection/hand-drawn-arrows-4/

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Type a quote here. A SIMPLE FUNCTION COMPONENT const HelloMessage = (props) => (
Hello {props.name}
); ReactDOM.render( , document.getElementById('hello-example') );

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Type a quote here. A SIMPLE CLASS COMPONENT class HelloMessage extends React.Component { render() { return (
Hello {this.props.name}
); } } ReactDOM.render( , document.getElementById('hello-example') );

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NEITHER MODEL REALLY CAPTURES REACT.

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https://dan.church

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dan abramov WHAT'S A COMPONENT WHY ARE THESE MODELS INSUFFICIENT TO DESCRIBE REACT?

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dan abramov WHAT'S A COMPONENT “PURE FUNCTION” MODEL DOESN’T DESCRIBE LOCAL STATE WHICH IS AN ESSENTIAL REACT FEATURE.

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dan abramov WHAT'S A COMPONENT “CLASS” MODEL DOESN’T EXPLAIN PURE-ISH RENDER, DISAWOVING INHERITANCE, LACK OF DIRECT INSTANTIATION, AND “RECEIVING” PROPS.

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@cedmax EMAIL: NAME marco WEBSITE cedmax.com TWITTER PRONOUNS: HE/HIM

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WE'RE ARE GOING TO TALK ABOUT COLOURS

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Type a quote here. export default class App extends Component { state = { colors: originalList, currentFilter: "", currentSortBy: "name", style: { ...constants, color: "black", background: "white" }, }; sortBy = sortBy => { this.setState({ currentSortBy: sortBy, colors: sorters[sortBy](this.state.colors), }); }; filter = currentFilter=> { const colors = getFilteredColours(originalList, currentFilter); this.setState({ currentFilter, colors }); }; COMPONENT STRUCTURE

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Type a quote here. onColorChange = hex => { this.setState({ style: { ...this.state.style, background: hex, color: getMostReadable(hex), }, }); }; return ( ); }; COMPONENT STRUCTURE

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LET'S CODE

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HOOKS

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1. OPT-IN 2. 100% BACKWARDS-COMPATIBLE 3. AVAILABLE NOW 
 HOOKS WERE RELEASED WITH REACT V16.8.0. react docs A JAVASCRIPT LIBRARY FOR BUILDING USER INTERFACES

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USESTATE

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const [colors, setColors] = useState(originalList); USESTATE ARRAY DEFAULT VALUE VALUE FUNCTION TO SET THE STATE

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const [colors, setColors] = useState(originalList); setColors(sortingFunction); CAN TAKE A FUNCTION... ARRAY DEFAULT VALUE VALUE FUNCTION TO SET THE STATE USESTATE

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const [colors, setColors] = useState(originalList); setColors(sortingFunction); CAN TAKE A FUNCTION... ... AND SO DOES USE STATE ARRAY DEFAULT VALUE VALUE FUNCTION TO SET THE STATE USESTATE

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const [colors, setColors] = useState(originalList); setColors(sortingFunction); setColors(sortingFunction(colors)); THEY ARE EXACTLY THE SAME ARRAY DEFAULT VALUE VALUE FUNCTION TO SET THE STATE CAN TAKE A FUNCTION... ... AND SO DOES USE STATE USESTATE

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setCurrentFilter(currentFilter); setColors(colors); COMPONENTS UPDATES GET ENQUEUED USESTATE

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USECALLBACK

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const sortBy = useCallback(e => { const { value: sortBy } = e.target; const sortingFunction = sorters[sortBy]; setColors(sortingFunction); }, []); USECALLBACK WRAPS A FUNCTION RETURNING
 A MEMOIZED VERSION

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USEREDUCER

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export default () => { const [colors, setColors] = useState(originalList); const [currentFilter, setCurrentFilter] = useState(""); const [currentSortBy, setCurrentSortBy] = useState("name"); const [style, setStyle] = useState({ ...constants, color: "black", background: "white", }); const sortBy = useCallback(sortBy => { const sortingFunction = sorters[sortBy]; setCurrentSortBy(sortBy); setColors(sortingFunction); }, []); const filter = useCallback(currentFilter => { const colors = getFilteredColors(originalList, currentFilter); setCurrentFilter(currentFilter); setColors(colors); }, []); STILL QUITE BUSY

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const onColorChange = useCallback(hex => { setStyle({ ...style, background: hex, color: getMostReadable(hex), }); }, []); return ( ); }; STILL QUITE BUSY

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const [state, dispatch] = useReducer(reducer, defaultState); USEREDUCER ARRAY DEFAULT VALUE VALUE REDUCERS

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export default (state, { type, payload }) => { switch (type) { case "filter": return { ...state, currentFilter: payload, colors: getFilteredColors(state.allColors, payload), }; case "sort": return { ...state, currentSortBy: payload, colors: sorters[payload](state.colors), }; case "change": return { ...state, style: { ...state.style, background: payload, color: getMostReadable(payload), }, }; default: return state; } }; USEREDUCER

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const [state, dispatch] = useReducer(reducer, defaultState); const emit = useCallback((type, payload) => dispatch({type, payload}), []); const sortBy = useCallback(sortBy => emit("sort", sortBy), []); const filter = useCallback(filter => emit("filter", filter), []); const onColorChange = useCallback(hex => emit("change", hex), []); USEREDUCER

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const [state, dispatch] = useReducer(reducer, defaultState); const emit = useCallback((type, payload) => dispatch({type, payload}), []); const sortBy = useCallback(sortBy => emit("sort", sortBy), []); const filter = useCallback(filter => emit("filter", filter), []); const onColorChange = useCallback(hex => emit("change", hex), []); USEREDUCER

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export default () => { const [state, dispatch] = useReducer(reducers, defaultState); const emit = useCallback((type, payload) => dispatch({ type, payload }), []); const sortBy = useCallback(sortBy => emit("sort", sortBy), []); const filter = useCallback(filter => emit("filter", filter), []); const onColorChange = useCallback(hex => emit("change", hex), []); return ( ); }; USEREDUCER

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USEEFFECT

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ACCEPTS A FUNCTION THAT CONTAINS IMPERATIVE, POSSIBLY EFFECTFUL CODE. react docs USEEFFECT

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THINK OF EFFECTS AS AN ESCAPE HATCH FROM REACT’S PURELY FUNCTIONAL WORLD INTO THE IMPERATIVE WORLD. react docs USEEFFECT

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NETWORK (DATA FETCHING...), DOM OR WINDOW (TITLE UPDATES, SUBSCRIBE TO WINDOW RESIZE OR MOUSE EVENTS, ACCESS LOCAL STORAGE), LOGGING (ANALYTICS...)

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FETCHING DATA useEffect(() => { const fetchData = async () => { const { data } = await axios.get(`/api/colors/${props.id}`); setColor(data); }; fetchData(); }, [props.id]);

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FETCHING DATA NOT BEING ABLE TO USE AN ASYNC FUNCTION WAS QUITE A GOTCHA FOR ME useEffect(() => { const fetchData = async () => { const { data } = await axios.get(`/api/colors/${props.id}`); setColor(data); }; fetchData(); }, [props.id]);

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FETCHING DATA NOT BEING ABLE TO USE AN ASYNC FUNCTION WAS QUITE A GOTCHA FOR ME LIST OF DEPENDENCIES useEffect(() => { const fetchData = async () => { const { data } = await axios.get(`/api/colors/${props.id}`); setColor(data); }; fetchData(); }, [props.id]);

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REACT LIFECYCLES WITH HOOKS //componentDidMount useEffect(() => console.log('mounted'), []); //componentDidUnmount useEffect(() => () => { console.log('will unmount'); }, []); THE EMPTY DEPENDENCY LIST
 GUARANTEES IT'S EXECUTED ONLY ONCE NO MATTER THE NUMBER OF RE-RENDERS

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//componentDidMount useEffect(() => console.log('mounted'), []); //componentDidUnmount useEffect(() => () => { console.log('will unmount'); }, []); THE EMPTY DEPENDENCY LIST
 GUARANTEES IT'S EXECUTED ONLY ONCE NO MATTER THE NUMBER OF RE-RENDERS IF THE CALLBACK RETURNS A
 FUNCTION, IT WILL BE CALLED BEFORE THE COMPONENT IS REMOVED FROM THE UI. REACT LIFECYCLES WITH HOOKS

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THE QUESTION IS NOT "WHEN DOES THIS EFFECT RUN" 
 
 THE QUESTION IS "WITH WHICH STATE DOES THIS EFFECT SYNCHRONIZE WITH" ryan florence REACT LIFECYCLES WITH HOOKS

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useEffect(() => console.log('mounted')); useEffect(() => console.log(''), []); useEffect( () => console.log(`fetch ${props.id}`), [props.id] ); WHAT STATE THE EFFECT SYNCS TO? ALL STATE CHANGES

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useEffect(() => console.log('mounted')); useEffect(() => console.log(''), []); useEffect(
 () => console.log(`fetch ${props.id}`),
 [props.id]
 ); NO STATE CHANGES WHAT STATE THE EFFECT SYNCS TO? ALL STATE CHANGES

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useEffect(() => console.log('mounted')); useEffect(() => console.log(''), []); useEffect( () => console.log(`fetch ${props.id}`), [props.id] ); PROP ID CHANGES WHAT STATE THE EFFECT SYNCS TO? NO STATE CHANGES ALL STATE CHANGES

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UPDATE THE URL WITH USEEFFECT

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const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL MATCH URL TO STATE

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const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL MATCH URL TO STATE

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const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS MATCH URL TO STATE

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export const listenToHistory = callback => { const getQs = () => qs.parse(window.location.search); window.addEventListener("popstate", () => callback(getQs())); callback(getQs()); }; 
 listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); THE CALLBACK GETS INVOKED IMMEDIATELY AND IN RESPONSE OF ANY POPSTATE EVENT WITH THE PARAMETERS IN THE QUERYSTRING MATCH URL TO STATE

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export const listenToHistory = callback => { const getQs = () => qs.parse(window.location.search); window.addEventListener("popstate", () => callback(getQs())); callback(getQs()); }; listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); IN THE CALLBACK WE SET THE STATE FOR ANY
 CORRESPONDING PARAMETER IN THE URL THE CALLBACK GETS INVOKED IMMEDIATELY AND IN RESPONSE OF ANY POPSTATE EVENT WITH THE PARAMETERS IN THE QUERYSTRING MATCH URL TO STATE

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const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS MATCH URL TO STATE

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ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL MATCH URL TO STATE AND WE MAKE SURE IT HAPPENS 
 ONLY THE FIRST TIME

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ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL MATCH URL TO STATE AND WE MAKE SURE IT HAPPENS 
 ONLY THE FIRST TIME AFTER THAT SETUP, WE CAN PUSH THE STATE CHANGES TO THE HISTORY

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window.history.pushState({}, "", `?${qs.stringify(qsObj)}`); MATCH URL TO STATE

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const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); MATCH URL TO STATE

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LET'S SEE IT WORKING

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CUSTOM HOOKS

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CUSTOM HOOK useQueryString( { currentSortBy, currentFilter }, { currentSortBy: sortBy, currentFilter: filter }, { currentSortBy: defaultSortBy, currentFilter: defaultFilter } );

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useQueryString( { currentSortBy, currentFilter }, { currentSortBy: sortBy, currentFilter: filter }, { currentSortBy: defaultSortBy, currentFilter: defaultFilter } ); CUSTOM HOOK VALUES

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useQueryString( { currentSortBy, currentFilter }, { currentSortBy: sortBy, currentFilter: filter }, { currentSortBy: defaultSortBy, currentFilter: defaultFilter } ); VALUES SETTERS, MATCHING 
 THE VALUES KEYS CUSTOM HOOK

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useQueryString( { currentSortBy, currentFilter }, { currentSortBy: sortBy, currentFilter: filter }, { currentSortBy: defaultSortBy, currentFilter: defaultFilter } ); VALUES SETTERS, MATCHING 
 THE VALUES KEYS CUSTOM HOOK DEFAULT VALUES, MATCHING 
 THE VALUES KEYS

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VALUES SETTERS useQueryString( [currentSortBy, sortBy, defaultSortBy], [currentFilter, filter, defaultFilter], ); CUSTOM HOOK useQueryString( { currentSortBy, currentFilter }, { currentSortBy: sortBy, currentFilter: filter }, { currentSortBy: defaultSortBy, currentFilter: defaultFilter } ); DEFAULTS

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const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); }; CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, [currentSortBy, currentFilter]); }; OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, Object.values(values)); }; OUR DEPENDENCIES ARE THE VALUES
 WE WANT TO PERSIST IN THE URL CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { const { currentFilter, currentSortBy } = data; // from the URL sortBy(currentSortBy || defaultSortBy); filter(currentFilter || defaultFilter); }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, Object.values(values)); }; ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; // in the URL setters[k](value || defaults[k]); })}); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, Object.values(values)); }; ON FIRST LOAD WE NEED TO RESTORE
 THE STATE FROM THE URL AND SUBSCRIBE 
 TO THE HISTORY EVENTS CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; // in the URL setters[k](value || defaults[k]); }) }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, Object.values(values)); }; CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; // in the URL setters[k](value || defaults[k]); }) }); setUrlRestored(true); } else { objectToHistory({ currentSortBy, currentFilter, }); } }, Object.values(values)); }; CUSTOM HOOK AFTER THAT SETUP, WE CAN PUSH THE STATE CHANGES TO THE HISTORY

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; // in the URL setters[k](value || defaults[k]); }) }); setUrlRestored(true); } else { objectToHistory(values); } }, Object.values(values)); }; CUSTOM HOOK AFTER THAT SETUP, WE CAN PUSH THE STATE CHANGES TO THE HISTORY

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; // in the URL setters[k](value || defaults[k]); }) }); setUrlRestored(true); } else { objectToHistory(values); } }, Object.values(values)); }; CUSTOM HOOK

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export const useQueryString = (values, setters, defaults) => { const [urlRestored, setUrlRestored] = useState(false); useEffect(() => { if (!urlRestored) { listenToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; // in the URL setters[k](value || defaults[k]); }) }); setUrlRestored(true); } else { objectToHistory(values); } }, Object.values(values)); }; ABSTRACTION ABSTRACTION ABSTRACTION CUSTOM HOOK

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LET'S MAKE SURE IT'S STILL WORKING

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A STEP FORWARD

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; CUSTOM HOOK WE COULD STORE THE LISTENER
 INSTEAD OF A BOOLEAN

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; CUSTOM HOOK HAVE THE SUBSCRIBER RETURNING THE LISTENER WE COULD STORE THE LISTENER
 INSTEAD OF A BOOLEAN

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; CUSTOM HOOK STORE THE LISTENER IN THE STATE WE COULD STORE THE LISTENER
 INSTEAD OF A BOOLEAN HAVE THE SUBSCRIBER RETURNING THE LISTENER

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; CUSTOM HOOK STORE THE LISTENER IN THE STATE WE COULD STORE THE LISTENER
 INSTEAD OF A BOOLEAN RETURN A FUNCTION TO CLEAR THE EFFECT, UNSUBSCRIBING FROM THE HISTORY EVENTS HAVE THE SUBSCRIBER RETURNING THE LISTENER

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; CUSTOM HOOK

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export default () => { const [state, dispatch] = useReducer(reducers, defaultState); const emit = useCallback((type, payload) => dispatch({ type, payload }), []); const sortBy = useCallback(sortBy => emit("sort", sortBy), []); const filter = useCallback(filter => emit("filter", filter), []); const onColorChange = useCallback(hex => emit("change", hex), []); useQueryString( { currentSortBy: state.currentSortBy, currentFilter: state.currentFilter }, { currentSortBy: sortBy, currentFilter: filter }, defaultState ); return ( ); }; USEREDUCER

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; CUSTOM HOOK

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CUSTOM HOOKS
 TESTING

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; TESTING

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export const useQueryString = (values, setters, defaults) => { const [historyListener, setHistoryListener] = useState(null); useEffect(() => { if (!historyListener) { const listener = subscribeToHistory(data => { Object.keys(values).forEach(k => { const value = data[k]; setters[k](value || defaults[k]); }); }); setHistoryListener(() => listener); } else { objectToHistory(values); } return () => unsubscribeFromHistory(historyListener); }, Object.values(values)); }; TESTING

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jest.mock("./utils", () => ({ objectToHistory: jest.fn(), subscribeToHistory: jest.fn(() => "listener function"), unsubscribeFromHistory: jest.fn(), }));
 
 const stateSetter = jest.fn(); const Component = ({ value }) => { useQueryString( { value }, { value: stateSetter }, { value: "defaultValue" } ); return null; }; TESTING

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jest.mock("./utils", () => ({ objectToHistory: jest.fn(), subscribeToHistory: jest.fn(() => "listener function"), unsubscribeFromHistory: jest.fn(), })); 
 const stateSetter = jest.fn(); const Component = ({ value }) => { useQueryString( { value }, { value: stateSetter }, { value: "defaultValue" } ); return null; }; TESTING

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test("the first time: subscribe to history with the right callback", () => { mount(); expect(subscribeToHistory).toBeCalledTimes(1); const popStateListener = subscribeToHistory.mock.calls[0][0]; popStateListener({ value: "a" }); expect(stateSetter).toBeCalledWith("a"); callback({ value: "" }); expect(stateSetter).toBeCalledWith("defaultValue"); }); TESTING

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test("the first time: subscribe to history with the right callback", () => { mount(); expect(subscribeToHistory).toBeCalledTimes(1); const popStateListener = subscribeToHistory.mock.calls[0][0]; popStateListener({ value: "b" }); expect(stateSetter).toBeCalledWith("b"); callback({ value: "" }); expect(stateSetter).toBeCalledWith("defaultValue"); }); TESTING

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test("the first time: subscribe to history with the right callback", () => { mount(); expect(subscribeToHistory).toBeCalledTimes(1); const popStateListener = subscribeToHistory.mock.calls[0][0]; popStateListener({ value: "b" }); expect(stateSetter).toBeCalledWith("b"); callback({ value: "" }); expect(stateSetter).toBeCalledWith("defaultValue"); }); TESTING

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const wrapper = mount(); test("further executions should invoke objectToHistory", () => { wrapper.setProps({ value: "b" }); expect(subscribeToHistory).toBeCalledTimes(0); expect(objectToHistory).toBeCalledTimes(1); }); test("further executions with the same props should do nothing", () => { wrapper.setProps({ value: "b" }); expect(subscribeToHistory).toBeCalledTimes(0); expect(objectToHistory).toBeCalledTimes(0); }); test("unmounting should invoke unsubscribeFromHistory", () => { wrapper.unmount(); expect(unsubscribeFromHistory).toBeCalledTimes(1); expect(unsubscribeFromHistory).toBeCalledWith("listener function"); }); TESTING

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const wrapper = mount(); test("further executions should invoke objectToHistory", () => { wrapper.setProps({ value: "b" }); expect(subscribeToHistory).toBeCalledTimes(0); expect(objectToHistory).toBeCalledTimes(1); }); test("further executions with the same props should do nothing", () => { wrapper.setProps({ value: "b" }); expect(subscribeToHistory).toBeCalledTimes(0); expect(objectToHistory).toBeCalledTimes(0); }); test("unmounting should invoke unsubscribeFromHistory", () => { wrapper.unmount(); expect(unsubscribeFromHistory).toBeCalledTimes(1); expect(unsubscribeFromHistory).toBeCalledWith("listener function"); }); TESTING

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const wrapper = mount(); test("further executions should invoke objectToHistory", () => { wrapper.setProps({ value: "b" }); expect(subscribeToHistory).toBeCalledTimes(0); expect(objectToHistory).toBeCalledTimes(1); }); test("further executions with the same props should do nothing", () => { wrapper.setProps({ value: "b" }); expect(subscribeToHistory).toBeCalledTimes(0); expect(objectToHistory).toBeCalledTimes(0); }); test("unmounting should invoke unsubscribeFromHistory", () => { wrapper.unmount(); expect(unsubscribeFromHistory).toBeCalledTimes(1); expect(unsubscribeFromHistory).toBeCalledWith("listener function"); }); TESTING

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FAQS

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WHY HOOKS AGAIN?

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THEY PROVIDE A BETTER MENTAL MODEL OF WHAT A COMPONENT IS. WHY HOOKS AGAIN?

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WITHOUT HOOKS: 46.15KB
 WITH HOOKS: 45.69KB ~0.5KB REMOVING 1 CLASS WHY HOOKS AGAIN?

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ARE THEY STABLE?

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YES AND NO: THE BASIC ONES PROBABLY YES, BUT THEY MIGHT EVOLVE A BIT ARE THEY STABLE?

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ARE THEY STABLE? INTENTIONALLY UNDERSPECIFYING DEPENDENCIES PASSED TO `USEEFFECT`/`USEMEMO` IS THE `ANY` OF REACT HOOKS. YOU THINK YOU'RE BEING CLEVER BY PASSING AN EMPTY ARRAY, BUT YOU'RE PROBABLY WRONG. INTENTIONALLY UNDERSPECIFYING DEPENDENCIES PASSED TO `USEEFFECT`/`USEMEMO` IS THE `ANY` OF REACT HOOKS. YOU THINK YOU'RE BEING CLEVER BY PASSING AN EMPTY ARRAY, BUT YOU'RE PROBABLY WRONG.

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ARE THEY STABLE? INTENTIONALLY UNDERSPECIFYING DEPENDENCIES PASSED TO `USEEFFECT`/`USEMEMO` IS THE `ANY` OF REACT HOOKS. YOU THINK YOU'RE BEING CLEVER BY PASSING AN EMPTY ARRAY, BUT YOU'RE PROBABLY WRONG. INTENTIONALLY UNDERSPECIFYING DEPENDENCIES PASSED TO `USEEFFECT`/`USEMEMO` IS THE `ANY` OF REACT HOOKS. YOU THINK YOU'RE BEING CLEVER BY PASSING AN EMPTY ARRAY, BUT YOU'RE PROBABLY WRONG.

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ARE THERE MORE HOOKS?

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YES! A FEW MORE COME WITH REACT & CUSTOM ONES, COMMUNITY DRIVEN ARE THERE MORE HOOKS?

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SHOULD I START USING THEM NOW?

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UP TO YOU, BUT THEY ARE AVAILABLE TO USE SINCE REACT V16.8.0 SHOULD I START USING THEM NOW?

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ARE CLASSES DISAPPEARING?

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NOT IN THE FORESEEABLE FUTURE: THE REACT TEAM WAS CLEAR ABOUT IT ARE CLASSES DISAPPEARING?

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WHAT'S THE MOST IMPORTANT TAKE AWAY?

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WHAT'S THE MOST IMPORTANT TAKE AWAY?

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colours.dsgn.it
 github.com/cedmax/colours overreacted.io
 dan abramov's blog usehooks.com
 code examples hooks.guide
 collection of React hooks reactjs.com
 official documentation marco@cedmax.com http://cedmax.com @cedmax