Last active
March 12, 2022 05:48
-
-
Save gragland/fe89992181663d5e46d024dec8a8e5e6 to your computer and use it in GitHub Desktop.
React Hook recipe from https://usehooks.com. Demo: https://codesandbox.io/s/kx83n7201o
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import { useState, useEffect, useRef } from 'react'; | |
// Let's pretend this <Counter> component is expensive to re-render so ... | |
// ... we wrap with React.memo, but we're still seeing performance issues :/ | |
// So we add useWhyDidYouUpdate and check our console to see what's going on. | |
const Counter = React.memo(props => { | |
useWhyDidYouUpdate('Counter', props); | |
return <div style={props.style}>{props.count}</div>; | |
}); | |
function App() { | |
const [count, setCount] = useState(0); | |
const [userId, setUserId] = useState(0); | |
// Our console output tells use that the style prop for <Counter> ... | |
// ... changes on every render, even when we only change userId state by ... | |
// ... clicking the "switch user" button. Oh of course! That's because the | |
// ... counterStyle object is being re-created on every render. | |
// Thanks to our hook we figured this out and realized we should probably ... | |
// ... move this object outside of the component body. | |
const counterStyle = { | |
fontSize: '3rem', | |
color: 'red' | |
}; | |
return ( | |
<div> | |
<div className="counter"> | |
<Counter count={count} style={counterStyle} /> | |
<button onClick={() => setCount(count + 1)}>Increment</button> | |
</div> | |
<div className="user"> | |
<img src={`http://i.pravatar.cc/80?img=${userId}`} /> | |
<button onClick={() => setUserId(userId + 1)}>Switch User</button> | |
</div> | |
</div> | |
); | |
} | |
// Hook | |
function useWhyDidYouUpdate(name, props) { | |
// Get a mutable ref object where we can store props ... | |
// ... for comparison next time this hook runs. | |
const previousProps = useRef(); | |
useEffect(() => { | |
if (previousProps.current) { | |
// Get all keys from previous and current props | |
const allKeys = Object.keys({ ...previousProps.current, ...props }); | |
// Use this object to keep track of changed props | |
const changesObj = {}; | |
// Iterate through keys | |
allKeys.forEach(key => { | |
// If previous is different from current | |
if (previousProps.current[key] !== props[key]) { | |
// Add to changesObj | |
changesObj[key] = { | |
from: previousProps.current[key], | |
to: props[key] | |
}; | |
} | |
}); | |
// If changesObj not empty then output to console | |
if (Object.keys(changesObj).length) { | |
console.log('[why-did-you-update]', name, changesObj); | |
} | |
} | |
// Finally update previousProps with current props for next hook call | |
previousProps.current = props; | |
}); | |
} |
@gragland You are right. I was thinking more of a solution to log exactly which props have changed. So it shows you more clearly how your app is behaving. I was not thinking about reference, but more of the data itself.
In conclusion, I was thinking about a different hook. But is nice to see it can be easily derive from your example.
Great work with useHooks by the way! =)
@davidpn11: Gotcha, makes sense and seems like a good way to extend this hook. Thanks for the kind words!
I'm happy if someone could turn the snippet into typescipt.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
@davidpn11 Maybe I'm missing something, but isn't the point that it does log every time there is a re-render? Why skip doing it when the avatar changes? Also, could you explain rationale behind
isEqual
? Not seeing why a simplepreviousProps.current[key] !== props[key]
isn't enough, since we just want to compare references to see if they changed (and thus caused a re-render).