The useImperativeHandle hook in React is used to customize the instance value that is exposed when using ref with a functional component. It is often used to expose specific methods or properties to the parent component via ref, rather than the entire instance of the component.

By default, React exposes the DOM node (or component instance) when using ref, but sometimes you want to expose only certain methods or properties to the parent. useImperativeHandle allows you to do this by modifying the value returned by ref.

Syntax:

• ref: The ref object that is passed down from the parent.
• createHandle: A function that returns an object with methods or properties to expose to the parent.
• dependencies: An optional array of dependencies to re-run the createHandle function.

Example Usage:

Let’s say you have a CustomInput component, and you want to allow the parent component to focus on the input field using a ref.

import React, { useRef, useImperativeHandle, forwardRef } from 'react';

// CustomInput component that forwards a ref
const CustomInput = forwardRef((props, ref) => {
const inputRef = useRef();

// useImperativeHandle allows you to customize what the parent can access
useImperativeHandle(ref, () => ({
focus: () => {
inputRef.current.focus();
},
clear: () => {
inputRef.current.value = '';
}
}));

return <input ref={inputRef} />;
});

function ParentComponent() {
const inputRef = useRef();

const handleFocus = () => {
inputRef.current.focus();
};

const handleClear = () => {
inputRef.current.clear();
};

return (
<div>
<CustomInput ref={inputRef} />
<button onClick={handleFocus}>Focus Input</button>
<button onClick={handleClear}>Clear Input</button>
</div>
);
}

export default ParentComponent;

How It Works:

1. CustomInput Component:

   • We use forwardRef to forward the ref to the CustomInput component.
   • Inside CustomInput, we use the useRef hook to reference the actual input element.
   • We then use useImperativeHandle to expose a custom focus and clear method to the parent component, so when the parent accesses the ref, it can call these methods directly.

2. ParentComponent:

   • We create a ref using useRef() and pass it down to CustomInput.
   • The parent can call focus and clear on the ref to manipulate the input field without directly accessing the DOM node.

Key Points:

• useImperativeHandle is used to control the value that is exposed to the parent when using ref in functional components.
• It’s typically used with forwardRef to forward a ref to the child component.
• You can expose only the methods or properties that are needed by the parent, preventing unnecessary exposure of internal state or methods.

When to use it?

• You need to expose only certain methods or properties to the parent component.
• You want to manage external control over a child component (like focusing or resetting an input field) while keeping internal logic private.

In most cases, you’ll rely on the default behavior of ref, but useImperativeHandle is helpful when you want to have more fine-grained control over the exposed ref behavior.