React useMergeState Hook
index.html
and script.js
have already been provided in the VM. In general, you only need to add code to script.js
and style.css
.
To create a stateful value and a function to update it by merging the new state provided, use the useState()
hook to create a state variable and initialize it to initialState
. Create a function that will update the state variable by merging the new state provided with the existing one. If the new state is a function, call it with the previous state as the argument and use the result. If no argument is provided, the state variable will be initialized with an empty object ({}
). The following code demonstrates how to implement this using the useMergeState
custom hook:
const useMergeState = (initialState = {}) => {
const [value, setValue] = React.useState(initialState);
const mergeState = (newState) => {
if (typeof newState === "function") {
newState = newState(value);
}
setValue({ ...value, ...newState });
};
return [value, mergeState];
};
Here is an example usage of the useMergeState
hook in a component named MyApp
:
const MyApp = () => {
const [data, setData] = useMergeState({ name: "John", age: 20 });
return (
<>
<input
value={data.name}
onChange={(e) => setData({ name: e.target.value })}
/>
<button onClick={() => setData(({ age }) => ({ age: age - 1 }))}>
-
</button>
{data.age}
<button onClick={() => setData(({ age }) => ({ age: age + 1 }))}>
+
</button>
</>
);
};
ReactDOM.createRoot(document.getElementById("root")).render(<MyApp />);
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