مدونة مقالة للمعلوميات

When Does the Component Execute the useEffect Method?

The useEffect hook in React runs after the component renders. Depending on the dependencies provided, it can execute in different scenarios:

1. With every state modification (No dependency array)

useEffect(() => {
    console.log("Component updated!");
});
        

Runs after every render (both initial render and updates).

2. Only when it's first rendered (Empty dependency array [])

useEffect(() => {
    console.log("Component mounted!");
}, []);
        

Runs only once, when the component mounts.

3. When specific dependencies change

useEffect(() => {
    console.log("State changed!");
}, [count]);
        

Runs only when the count variable changes.

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Will It Work If We Remove the Dependency Array [] From the useEffect Function?

Answer: True

If you remove the dependency array, useEffect() will run after every render, which can cause performance issues.

useEffect(() => {
    console.log("Runs after every render!");
});
        

What Happens in Different Cases?

• No dependency array → Runs after every render (state or props changes).
• Empty array [] → Runs only on mount.
• Specific dependencies [count] → Runs when count changes.

Using [] ensures that useEffect only runs once (when the component mounts). Without it, the function will continuously execute whenever the component updates.

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What Should We Add as a Secondary Parameter Inside the useEffect Method for a Spinner?

Answer: [] (Empty Dependency Array)

When fetching data and using a spinner, we only want the effect to run once (on mount). This is achieved by passing [] as the second argument.

Example of Loading Spinner with useEffect:

import { useState, useEffect } from "react";

function App() {
    const [data, setData] = useState(null);
    const [loading, setLoading] = useState(true);

    useEffect(() => {
        fetch("https://jsonplaceholder.typicode.com/posts/1")
            .then((response) => response.json())
            .then((data) => {
                setData(data);
                setLoading(false); // Hide spinner after data is loaded
            });
    }, []); // 👈 Runs only once when component mounts

    return (
        

            {loading ? 
Loading...
 : 
{data.title}
}
        
    );
}

export default App;
        

Why []?

• Ensures fetch request runs only once when the component mounts.
• Prevents infinite API calls that could happen if useEffect runs on every render.

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Conclusion

The useEffect hook is a powerful tool for handling side effects in React. Understanding how it works helps prevent performance issues and ensures efficient component behavior. Always use the correct dependency array configuration depending on your needs!