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:

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useLayoutEffect – Synchronous side effects
useImperativeHandle – Controlling ref exposure
useDebugValue – 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

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