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Start your free trialSimon Coates
8,377 PointsIs there are reason to use useRef for the solution rather than just using a normal javascript variable?
Unless I'm missing something, couldn't you use a normal javascript variable and save yourself a rerender? Something like:
import React, { useState, useRef } from "react";
import Header from './Header';
import Player from "./Player";
import AddPlayerForm from "./AddPlayerForm";
const App = () => {
const [players, setPlayers] = useState([
{
name: "Guil",
score: 0,
id: 1
},
{
name: "Treasure",
score: 0,
id: 2
},
{
name: "Ashley",
score: 0,
id: 3
},
{
name: "James",
score: 0,
id: 4
}
]);
const nextPlayerId = useRef(5);
const scores = players.map(p => p.score);
const highScore = Math.max(...scores);
const handleRemovePlayer = (id) => {
setPlayers(prevPlayers => prevPlayers.filter(p => p.id !== id));
}
const handleScoreChange = (id, delta) => {
setPlayers(prevPlayers => prevPlayers.map(player => {
if (player.id === id) {
return {
name: player.name,
score: player.score + delta,
id: player.id
}
}
return player;
}));
}
const handleAddPlayer = (name) => {
setPlayers(prevPlayers => [
...prevPlayers,
{
name,
score: 0,
id: nextPlayerId.current++
}
]);
}
return (
<div className="scoreboard">
<Header
players={players}
/>
{/* Players list */}
{players.map(player =>
<Player
name={player.name}
score={player.score}
id={player.id}
key={player.id.toString()}
removePlayer={handleRemovePlayer}
changeScore={handleScoreChange}
isHighScore={player.score === highScore}
/>
)}
<AddPlayerForm addPlayer={handleAddPlayer} />
</div>
);
}
export default App;
I'm just concerned I'm missing something terribly important. If anyone has any insight, I'd appreciate it.
1 Answer
Clayton Perszyk
Treehouse Moderator 48,850 PointsI believe it is because the nextPlayerId is not used in the component's view, so you don't want to cause a re-render of the view and any possible children... If you used a variable and update it, it will cause a re-render...
In short it's used to prevent re-rendering.
Additional details:
- Only update variables when necessary. Unnecessary re-renders can slow down your application.
- You can also use the useMemo and useCallback hooks to prevent unnecessary re-renders. (although they're use cases are different than useRef)
Simon Coates
8,377 PointsSimon Coates
8,377 PointsAny update to App state that would alter the value of a Player highscore attribute already triggers a rerender. Then 'highScore' variable is only local and shouldn't alter anything in terms of rerenders, I wouldn't have thought. Sorry for not getting back to you at the time. I didn't really understand what you were getting at and just had that general sense that my brain was melting. But I rewatched the series today and wound up writing the same solution (more or less). It's nice to hit a particular wall and then 8 months later find myself beating my head on the same spot.