In useEffect, what’s the difference between providing no dependency array and an empty one?

When working with React and its useEffect hook, you may come across the scenario where you need to specify a dependency array. This array tells React which variables or values the effect depends on, so that it can re-run the effect whenever any of those dependencies change.

However, there are two options when it comes to specifying the dependency array: providing no dependency array at all, or providing an empty one. Let’s explore the difference between these two approaches.

No Dependency Array

When you don’t provide a dependency array, it means that the effect will run after every render. This can be useful in certain cases where you want the effect to be executed whenever any state or prop changes. However, it can also lead to unnecessary re-renders and performance issues if not used carefully.

Here’s an example of using useEffect without a dependency array:

{`useEffect(() => {
  // Effect code here
});`}

In this case, the effect will run after every render, regardless of any dependencies. This can be useful for effects that don’t rely on any specific values and need to be executed on every render.

Empty Dependency Array

On the other hand, providing an empty dependency array means that the effect will only run once, after the initial render. It will not re-run if any state or prop changes.

This approach is commonly used for effects that need to be executed only once, such as fetching data from an API or subscribing to an event listener.

Here’s an example of using useEffect with an empty dependency array:

{`useEffect(() => {
  // Effect code here
}, []);`}

In this case, the effect will run only once, after the initial render. It won’t be re-run even if any state or prop changes.

Conclusion

So, to summarize:

• Providing no dependency array means the effect will run after every render.
• Providing an empty dependency array means the effect will run only once, after the initial render.

Choose the approach that best suits your use case. If you need the effect to run on every render, use no dependency array. If you need the effect to run only once, use an empty dependency array.

Remember to consider the performance implications and only use the appropriate approach for your specific scenario.