React useDelayedState 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 delay the creation of a stateful value until a condition is met, follow these steps:
- Use the
useState()
hook to create a stateful value containing the actual state
and a boolean, loaded
.
- Use the
useEffect()
hook to update the stateful value if the condition
or loaded
changes.
- Create a function,
updateState
, that only updates the state
value if loaded
is truthy.
const useDelayedState = (initialState, condition) => {
const [{ state, loaded }, setState] = React.useState({
state: null,
loaded: false
});
React.useEffect(() => {
if (!loaded && condition) setState({ state: initialState, loaded: true });
}, [condition, loaded]);
const updateState = (newState) => {
if (!loaded) return;
setState({ state: newState, loaded });
};
return [state, updateState];
};
Here's an example of how to use the useDelayedState
hook:
const App = () => {
const [branches, setBranches] = React.useState([]);
const [selectedBranch, setSelectedBranch] = useDelayedState(
branches[0],
branches.length
);
React.useEffect(() => {
const handle = setTimeout(() => {
setBranches(["master", "staging", "test", "dev"]);
}, 2000);
return () => {
handle && clearTimeout(handle);
};
}, []);
return (
<div>
<p>Selected branch: {selectedBranch}</p>
<select onChange={(e) => setSelectedBranch(e.target.value)}>
{branches.map((branch) => (
<option key={branch} value={branch}>
{branch}
</option>
))}
</select>
</div>
);
};
ReactDOM.createRoot(document.getElementById("root")).render(<App />);
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