React useDelayedState Hook

Introduction

In this lab, we will learn how to use the useDelayedState hook in React to delay the creation of a stateful value until a certain condition is met. This hook is useful when we need to wait for data or props to load before creating a stateful value, and can help improve the performance of our application. Through practical examples, we will see how this hook can be implemented and how it can be used to update stateful values in our React components.

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:

1. Use the useState() hook to create a stateful value containing the actual state and a boolean, loaded.
2. Use the useEffect() hook to update the stateful value if the condition or loaded changes.
3. 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 => setSelectedBranch(e.target.value)}>
        {branches.map((branch) => (
          <option key={branch} value={branch}>
            {branch}
          </option>
        ))}
      </select>
    </div>
  );
};

ReactDOM.createRoot(document.getElementById("root")).render(<App />);

Please click on 'Go Live' in the bottom right corner to run the web service on port 8080. Then, you can refresh the Web 8080 Tab to preview the web page.

Summary

Congratulations! You have completed the React useDelayedState Hook lab. You can practice more labs in LabEx to improve your skills.