Understanding the Reasoning
The rationale behind this rule lies in how React tracks and manages the state associated with hooks. React relies on the order in which hooks are called to maintain consistency between renders. By calling hooks at the top level, React can guarantee that the order of hooks remains unchanged across re-renders, ensuring predictable behavior and preventing bugs.
Example 1: Below is an example of hooks that only be called at top level of function component.
import React, { useEffect, useState } from 'react'
function App() {
const [count, setCount] = useState(0);
if (count > 10) {
useEffect(() => {
document.title = `Count: ${count}`;
}, [count]);
}
return (
<div>
<p>Count: {count}</p>
<button onClick={() => setCount(count + 1)}>
Increment
</button>
</div>
);
}
export default App
Output: In this example, the useEffect
hook is conditionally called based on the value of count
. While this might seem harmless at first glance, it violates the rule of calling hooks at the top level. As a result, React can’t reliably track the order of hooks across renders, potentially leading to bugs or unexpected behavior.
Example 2: To correct the usage of the useEffect
hook in your App
component, you need to move it outside the conditional statement so that it’s always called at the top level of the component. Here’s the corrected code:
import React, { useEffect, useState } from 'react';
function App() {
const [count, setCount] = useState(0);
// Move useEffect outside the conditional statement
useEffect(() => {
if (count > 10) {
document.title = `Count: ${count}`;
}
}, [count]);
return (
<div>
<p>Count: {count}</p>
<button onClick={
() => setCount(count + 1)}>
Increment
</button>
</div>
);
}
export default App;
Output:
Why should hooks only be called at the top level of a function component?
React has introduced an innovative feature called hooks in recent years. Hooks can be used by developers to use state and other React features in functional components, which makes the code simpler and more reusable. However, there is a crucial rule that developers must keep in mind while using hooks, which is that they should only be called at the top level of a function component. In this article, we will discuss the reasons behind this rule and understand why following it is important to maintain the functionality and integrity of React components.
Table of Content
- What are React Hooks?
- Benefits of Using Hooks
- Importance of Calling Hooks at the Top Level
- Understanding the Reasoning
- Conclusion