I need to reuse data in my app with hook, so I created a hook called useData
import { useState } from "react";
export default function useData() {
const [message, setMessage] = useState("");
const [type, setType] = useState("error");
return [{ message, type }, { setMessage, setType }];
}
And then I use my hook in my app like below.
function App() {
const [data, action] = useData();
const handleClick = () => {
action.setMessage("Hello message");
action.setType("info");
alert(JSON.stringify(data));
};
return (
<div className="App">
<h1>Hello CodeSandbox</h1>
<h2>Start editing to see some magic happen!</h2>
<button className="btn" onClick={handleClick}>
Alert Data
</button>
</div>
);
}
When I clicked the button Alert Data
at the first time it will alert
{message: "", type: "error"}
My expectation is
{message: "Hello message", type: "info"}
What am I doing it wrong here? Please let me know, and is there any way to fix this code?
Here's the codesandbox code: https://codesandbox.io/embed/romantic-hugle-zm2e2?fontsize=14&hidenavigation=1&theme=dark
Thanks for your attention.
You're counting on data
being updated the instant you call your onClick
handler, but that won't be true until the next render. Instead, consider using a useEffect
hook. In the following example, I've also created a stateful open
variable to tell the modal when to be open.
function App() {
const [data, action] = useData();
const [open, setOpen] = useState(false);
const handleClick = () => {
action.setMessage("Hello message");
action.setType("info");
setOpen(true);
};
useEffect(() => {
if (open) {
alert(JSON.stringify(data));
setOpen(false);
}
}, [open, data])
return (
<div className="App">
<h1>Hello CodeSandbox</h1>
<h2>Start editing to see some magic happen!</h2>
<button className="btn" onClick={handleClick}>
Alert Data
</button>
</div>
);
}
In React.js, setState isn't a synchronous function. That is, setState doesn't change the state instantly. For this case, setState has a version with the completion callback. You can define a custom Hook with the completion callback. Fortunately, there is an npm package called "use-state-with-callback".
Or you can write the code as follows.
useData.js
export default function useData(msg, cb) { const [message, setMessage] = useState(msg); useEffect(() => cb(message), [message]); return [message, setMessage]; }
index.js
function App() { const callback = (msg) => { alert(JSON.stringify(msg)); } const [message, setMessage] = useData({ content: "", type: "error" }, callback); const handleClick = () => { setMessage({ content: "Hello message", type: "info" }); }; return ( <div className="App"> <h1>Hello CodeSandbox</h1> <h2>Start editing to see some magic happen!</h2> <button className="btn" onClick={handleClick}> Alert Data </button> </div> ); } const rootElement = document.getElementById("root"); ReactDOM.render(<App />, rootElement);
This works fine.
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