目标:每次我按下“W+C+N”键时,屏幕上会随机出现一个图像。
实际结果:图像仅每两次按键出现一次。例如,如果我在“W+C+N”上按 4 次,只会出现 2 个新图像。
滥用我的
useEffect
,它要么来自:
import egg from "./logo.png";
import { useState, useEffect } from "react";
function App() {
let map = []; //array of keys to store
const [coordinates, setcoordinates] = useState([]); //array of image coordinates
const handleKey = (event) => {
onkeydown = onkeyup = function (event) {
map[event.keyCode] = event.type === "keydown";
};
//random image coordinates
if (map[87] && map[67] && map[78]) {
const newCoordinates = [...coordinates];
let random_left = Math.floor(Math.random() * window.innerWidth);
let random_top = Math.floor(Math.random() * window.innerHeight);
newCoordinates.push({ left: random_left, top: random_top });
setcoordinates(newCoordinates);
}
};
useEffect(() => {
window.addEventListener("keypress", handleKey);
return () => {
window.removeEventListener("keypress", handleKey);
};
}, [handleKey]);
return (
<div className="App">
<img src={egg} alt="o easter egg" />
<h1>Rocambole</h1>
<h2>Good luck!</h2>
{console.log(coordinates)}
{coordinates.map((item, index) => {
return (
<img
key={index}
src={egg}
alt="egg"
className="newImg"
style={{ top: `${item.top}px`, left: `${item.left}px` }}
/>
);
})}
</div>
);
}
export default App;
尝试用一个函数更新状态,这样你就可以确保注册在内存中的事件监听器每次都获得新鲜的状态,并且还可以将函数
handleKey
移到useEffect
中:
import egg from "./logo.png";
import { useState, useEffect } from "react";
function App() {
let map = []; //array of keys to store
const [coordinates, setcoordinates] = useState([]); //array of image coordinates
useEffect(() => {
const handleKey = (event) => {
onkeydown = onkeyup = function (event) {
map[event.keyCode] = event.type === "keydown";
};
//random image coordinates
if (map[87] && map[67] && map[78]) {
let random_left = Math.floor(Math.random() * window.innerWidth);
let random_top = Math.floor(Math.random() * window.innerHeight);
setcoordinates(coordinates =>[...coordinates, { left: random_left, top: random_top }]);
}
};
window.addEventListener("keypress", handleKey);
return () => {
window.removeEventListener("keypress", handleKey);
};
}, []);
return (
<div className="App">
<img src={egg} alt="o easter egg" />
<h1>Rocambole</h1>
<h2>Good luck!</h2>
{console.log(coordinates)}
{coordinates.map((item, index) => {
return (
<img
key={index}
src={egg}
alt="egg"
className="newImg"
style={{ top: `${item.top}px`, left: `${item.left}px` }}
/>
);
})}
</div>
);
}
export default App;