Specialized React Hooks
React provides several specialized hooks beyond the common useState, useEffect, and useContext. These hooks are used in advanced scenarios where you need precise control over DOM, component instances, or debugging custom hooks.
The main specialized hooks are:
useLayoutEffect– Synchronous side effectsuseImperativeHandle– Controlling ref exposureuseDebugValue– Debugging custom hooks
useLayoutEffect – Synchronous Side Effects
useLayoutEffect is similar to useEffect but runs synchronously after all DOM mutations and before the browser paints the UI.
When to Use
- Measuring DOM elements immediately after render
- Updating layout or styles based on DOM measurements
- Preventing visual flickers
Syntax:
useLayoutEffect(() => {
// Your code here
return () => {
// Cleanup
};
}, [dependencies]);
Example:
import React, { useRef, useLayoutEffect, useState } from "react";
function Box() {
const boxRef = useRef();
const [width, setWidth] = useState(0);
useLayoutEffect(() => {
setWidth(boxRef.current.offsetWidth);
}, []);
return (
<div>
<div ref={boxRef} style={{ width: "50%" }}>Resizable Box</div>
<p>Box width: {width}px</p>
</div>
);
}
useImperativeHandle – Controlling Ref Exposure
useImperativeHandle works with forwardRef to customize what values or methods are exposed to a parent component via a ref.
When to Use
- Exposing child component methods
- Hiding internal DOM implementation details
- Controlling interaction with parent components
Syntax:
useImperativeHandle(ref, () => ({
method1,
method2
}));
Example:
import React, { useRef, forwardRef, useImperativeHandle } from "react";
const CustomInput = forwardRef((props, ref) => {
const inputRef = useRef();
useImperativeHandle(ref, () => ({
focus: () => inputRef.current.focus()
}));
return <input ref={inputRef} />;
});
function App() {
const inputRef = useRef();
return (
<div>
<CustomInput ref={inputRef} />
<button onClick={() => inputRef.current.focus()}>Focus Input</button>
</div>
);
}
useDebugValue – Debugging Custom Hooks
useDebugValue allows displaying debug information for custom hooks in React DevTools. It does not affect runtime behavior but helps developers debug hooks easily.
Syntax:
useDebugValue(value);
Example:
import { useState, useEffect, useDebugValue } from "react";
function useOnlineStatus() {
const [isOnline, setIsOnline] = useState(navigator.onLine);
useEffect(() => {
const handleOnline = () => setIsOnline(true);
const handleOffline = () => setIsOnline(false);
window.addEventListener("online", handleOnline);
window.addEventListener("offline", handleOffline);
return () => {
window.removeEventListener("online", handleOnline);
window.removeEventListener("offline", handleOffline);
};
}, []);
useDebugValue(isOnline ? "Online" : "Offline");
return isOnline;
}
Summary of Specialized Hooks
| Hook | Purpose | Typical Use Case |
|---|---|---|
| useLayoutEffect | Run synchronous side effects after DOM mutations | Measuring DOM, layout adjustments, avoiding flicker |
| useImperativeHandle | Expose specific methods or properties to parent via ref | Child component APIs, encapsulation |
| useDebugValue | Display debug info for custom hooks in DevTools | Debugging complex custom hooks |