Updating and merging state object using React useState() hook
If anyone is searching for useState() hooks update for object
Through Input
const [state, setState] = useState({ fName: "", lName: "" }); const handleChange = e => { const { name, value } = e.target; setState(prevState => ({ ...prevState, [name]: value })); }; <input value={state.fName} type="text" onChange={handleChange} name="fName" /> <input value={state.lName} type="text" onChange={handleChange} name="lName" />
Through onSubmit or button click
setState(prevState => ({ ...prevState, fName: 'your updated value here' }));
Both options are valid, but just as with setState
in a class component you need to be careful when updating state derived from something that already is in state.
If you e.g. update a count twice in a row, it will not work as expected if you don't use the function version of updating the state.
const { useState } = React;
function App() {
const [count, setCount] = useState(0);
function brokenIncrement() {
setCount(count + 1);
setCount(count + 1);
}
function increment() {
setCount(count => count + 1);
setCount(count => count + 1);
}
return (
<div>
<div>{count}</div>
<button onClick={brokenIncrement}>Broken increment</button>
<button onClick={increment}>Increment</button>
</div>
);
}
ReactDOM.render(<App />, document.getElementById("root"));
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="root"></div>