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React Hooks
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Matija Marohnić
December 13, 2019
Programming
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React Hooks
Matija Marohnić
December 13, 2019
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Transcript
React Hooks
React Hooks • released in React 16.8 • a new
way to “hook into” React features • but first, let’s recap the API we have now
Class components
function MyComponent() { return <input type="email" "/> }
class MyComponent extends React.Component { state = { email: ''
} render() { return ( <input type="email" value={this.state.email} onChange={event "=> { this.setState({ email: event.target.value, }) }} "/> ); } }
function MyComponent({ value, onChange }) { return ( <input type="email"
value={value} onChange={onChange} "/> ) }
Pros • custom methods • reusing logic • naming logic
Cons • switching back and forth between functions and classes
• a lot of typing • noisy Git diffs • class components are weird • we don’t instantiate them • we don’t extend them
Lifecycle methods
class MyComponent extends React.Component { constructor(props) static getDerivedStateFromProps(props, state) render()
componentDidMount() shouldComponentUpdate(nextProps, nextState) getSnapshotBeforeUpdate(prevProps, prevState) componentDidUpdate(prevProps, prevState, snapshot) componentWillUnmount() }
Pros • transparency • descriptive method names • API is
well documented • fine-grained control • easily target exact moment in the lifecycle
Cons • no way to escape the complexity • memorizing
common pitfalls like endless loops • spreading a single feature across multiple methods
Higher-order components (HOCs)
import email from './hocs/email' function MyComponent({ email, handleEmailChange }) {
return ( <input type="email" value={email} onChange={handleEmailChange} "/> ) } export default email(MyComponent)
Pros • reusing complex behavior • we can keep using
function components
Cons • readability • all props are mixed together •
the HOC call is usually the last thing we see
Ok, back to hooks
None
Hooks • can only be used in function components •
they represent a new mental model
Lifecycle methods
Basic hooks • useState for local state • useEffect for
side-effects • useContext for applying context
import React from 'react' function MyComponent() { const [email, setEmail]
= React.useState('') return ( <input type="email" value={email} onChange={event "=> { setEmail(event.target.value) }} "/> ) }
Stateless or function components?
import React from 'react' function MyComponent() { React.useEffect(() "=> {
console.log('mounted') return () "=> { console.log('unmounted') } }, []) return "// ""... }
A must-read: A Complete Guide to useEffect by Dan Abramov
Additional hooks • useMemo for memoizing a computed value •
useCallback for memoizing a function reference • etc. https://reactjs.org/docs/hooks-reference.html
import React from 'react' import { computeExpensiveValue } from './utils/slow'
function MyComponent({ id }) { const value = React.useMemo(() "=> { return computeExpensiveValue(id) }, [id]) return "// ""... }
Read before memoizing • One simple trick to optimize React
re-renders • When to useMemo and useCallback
Custom hooks
import React from 'react' function useModal() { const CLASS_NAME =
'modal-open' React.useEffect(() "=> { document.body.classList.add(CLASS_NAME) return () "=> { document.body.classList.remove(CLASS_NAME) } }, []) }
Custom hooks recipes: usehooks.com
eslint-plugin-react-hooks
yarn install "--save-dev eslint-plugin-react-hooks module.exports = { plugins: [ 'react-hooks',
], rules: { 'react-hooks/rules-of-hooks': 'error', 'react-hooks/exhaustive-deps': 'warn', } }
None
import React from 'react' import AnotherComponent from './AnotherComponent' function MyComponent({
id }) { const onClick = React.useCallback(() "=> { "// do something with id }, [id]) return ( <AnotherComponent onClick={onClick} "/> ) }
const onClick = React.useCallback(() "=> { "// do something with
id }, [id])
const onClick = React.useMemo(() "=> { return () "=> {
"// do something with id } }, [id])
import React from 'react' import AnotherComponent from './AnotherComponent' function MyComponent({
id }) { const onClick = React.useCallback(() "=> { "// do something with id }, [id]) return ( <AnotherComponent onClick={onClick} "/> ) }
Does AnotherComponent need reference equality?
import React from 'react' function AnotherComponent({ onClick }) { "//
expensive rendering } export default React.memo(AnotherComponent)
Pros • less typing, more thinking • reusing behavior is
nicer • no need for classes anymore…?
Cons • unlearning lifecycle methods • are there any more
cons? that’s up to you
Questions? @silvenon