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No content
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Why do you need to…
Use unidirectional data flow
Avoid calling hooks conditionally
Store state using the useState hook
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Conditionally call React hooks
Build impure components
Pull in a second UI library
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About me
Senior Software Engineer building
Microsoft Loop
Worked on Edge, Chrome, and Firefox
React developer for 8+ years
tigeroakes.com
@notwoods.bsky.social
@not_woods
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The art of
best practices for
React performance
ignoring
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*
*
*
*
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CAUTION!
Use your best judgement, evaluate tradeoffs, and communicate.
Photo by Markus Spiske on Unsplash
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THE PLAN
01
When does
React rerender?
02
How to isolate
expensive hooks
Using impure
components
03
How to only update
leaf components
Using a different
UI library
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01
When does React
rerender?
Photo by Noah Boyer on Unsplash
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Every rerender starts with a
state change.
State
change
Component
re-renders
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Every rerender starts with a
state change.
State
change
Component
re-renders
Descendant
components
re-render
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function MyCounter() {
const [count, setCount] = useState(0);
const handleClick = () => setCount(count + 1);
return (
Increment
);
}
function Title() {
return # of rules broken
; } function CounterDisplay({ count }) { return {count}; }Slide 13
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function MyCounter() {
const [count, setCount] = useState(0);
const handleClick = () => setCount(count + 1);
return (
Increment
);
}
function Title() {
return # of rules broken
; } function CounterDisplay({ count }) { return {count}; }Slide 14
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function MyCounter() {
}
vs
# of rules broken
{1} Increment# of rules broken
{0} IncrementSlide 15
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App
MyCounter
state: count (0)
Title CounterDisplay
props: count
(1)
(2)
(3)
(4)
Increment
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App
MyCounter
state: count (0)
Title CounterDisplay
props: count
(1)
(2)
(3)
(4)
Increment
React.memo() React.memo()
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React Profiler:
Highlight renders
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React Profiler:
Highlight renders
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React Profiler:
Why did it render?
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https://www.joshwcomeau.com
/react/why-react-re-renders/
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Just always write
performant
components!
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Every rerender starts with a
state change.
State
change
Component
re-renders
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02
Isolating expensive
hooks
Isolate state changes with
side effect components
Photo by Sam Pearce-Warrilow on Unsplash
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function useGetData() {
const [state, setState] = useState();
useEffect(() => {
fetchData().then(setState);
}, []);
return state;
}
function App() {
const data = useGetData();
return ;
}
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function useGetData() {
const [state, setState] = useState();
const [otherState, setOtherState] = useState();
useEffect(() => {
fetchData().then(setState);
}, []);
useEffect(() => {
fetchOtherData(state.id).then(setOtherState);
}, [state.id]);
return otherState;
}
function App() {
const data = useGetData();
return ;
}
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function useGetData() {
const [otherState, setOtherState] = useState();
useEffect(() => {
fetchData()
.then(state => fetchOtherData(state.id))
.then(setOtherState)
}, []);
return otherState;
}
function App() {
const data = useGetData();
return ;
}
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function ExpensiveEffect(props) {
const otherState = useGetData();
useEffect(() => {
props.setState(otherState);
}, [otherState]);
return null;
}
function App() {
const [data, setData] = useState();
return <>
>;
}
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App
state: data
ExpensiveEffect
props: setState
UI
props: data
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5x speedup
Refactoring in Microsoft Loop
1x per state change
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return (
<>
{shouldLoad && (
)}
>
);
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const LazyExpensiveEffect = React.lazy(() =>
import('./ExpensiveEffect’)
);
return (
<>
>
);
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@Composable
fun loadData() {
val (state, setState) = remember { mutableStateOf() }
SideEffect {
fetchData().then(::setState)
}
return state
}
@Composable
fun App() { … }
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App
state: data
ExpensiveEffect
props: setState
UI
props: data
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03
Only updating
leaf components
Pull state management out of React
Photo by Jakob Rosen on Unsplash
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Sidebar
Item
Date
Item
Date
Item
Date
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useState
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Svelte
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import { writable } from 'svelte/store';
let store = writable(initialState);
store.set(newState);
store.update(oldState => newState);
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import {
writable,
derived,
} from 'svelte/store';
import {} from 'svelte';
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import { writable } from 'svelte/store';
function Sidebar(props) {
const store = React.useMemo(() => writable());
return <>
{props.items.map(item =>
)}
>
}
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import { writable } from 'svelte/store';
let store = writable(0);
store.set(1);
store === store;
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import { useSyncExternalStore } from 'react';
import { get } from 'svelte/store';
// useSyncExternalStore internally uses
// useState and useEffect
const state = useSyncExternalStore(
store.subscribe,
() => get(store)
);
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Sidebar
Item
skipped
Date
Item
skipped
Date
Item
skipped
Date
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Svelte Stores
● Store is a constant reference
passed around with props or
context.
● Store’s value can be changed
without re-rendering React tree.
● Translated into React state using
the useSyncExternalStore hook.
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function Sidebar(props) {
const store = React.useMemo(() => writable());
return <>
{props.items.map(item =>
)}
>
}
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import { writable, readable } from 'svelte/store';
class DataModel {
#state = writable();
get state() {
return readable(this.#state);
}
performUpdate() {
this.#state.set('done')
}
}
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Redux
● Store is a constant reference
passed around with .
● Store’s value can be changed
without re-rendering React tree.
● Translated into React state using
the useSelector hook.
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React.useReducer
● Reducer value is stored as one
giant React state object.
● Changing reducer’s value
will re-render React tree.
● State is translated at the top of the
React tree once, instead of in the
leaf components.
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Could you use
Signals?
Yes.
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import { readable } from 'svelte/store';
const mediaQuery = window.matchMedia('(max-width: 640px)');
const mediaQueryStore = readable(
mediaQuery.matches,
function onFirstListenerStart(set) {
const listener = () => set(mediaQuery.matches);
listener();
mediaQuery.addEventListener('change', listener);
// return cleanup function, similar to useEffect
return function onLastListenerStop() {
mediaQuery.removeEventListener('change', listener);
}
}
);
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No content
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CREDITS: This presentation template was created
by Slidesgo, and includes icons by Flaticon, and
infographics & images by Freepik
THANKS!
https://loop.microsoft.com
tigeroakes.com
@notwoods.bsky.social
@not_woods
Photo by Fabio Spinelli on Unsplash