useRef

What is useRef?

The useRef hook in React is used to access and interact with DOM elements directly or to keep a mutable value that does not cause re-renders when changed. It provides a way to persist values across renders without triggering a component update.

How useRef Works

useRef returns a mutable object called a "ref object" with a .current property. This property can hold a value that persists across re-renders.

Basic Syntax

const myRef = useRef(initialValue);

• initialValue: The initial value for the ref object. This is optional.

Example 1: Accessing DOM Elements

In this example, we'll use useRef to access a DOM element directly.

1. Create the Component

   import React, { useRef, useEffect } from 'react';

   const FocusInput = () => {
     // Create a ref with useRef
     const inputRef = useRef(null);

     useEffect(() => {
       // Focus the input field when the component mounts
       inputRef.current.focus();
     }, []);

     return (
       <div>
         <input ref={inputRef} type="text" placeholder="Focus me on mount" />
       </div>
     );
   };

   export default FocusInput;

Explanation:

• useRef(null) creates a ref object.
• inputRef.current gives access to the input element.
• useEffect is used to focus the input field when the component mounts.

Example 2: Keeping Mutable Values

In this example, we'll use useRef to keep a mutable value that does not cause re-renders when updated.

1. Create the Component

   import React, { useRef, useState } from 'react';

   const Timer = () => {
     const [count, setCount] = useState(0);
     const timerRef = useRef(null);

     const startTimer = () => {
       if (timerRef.current) {
         clearInterval(timerRef.current);
       }
       timerRef.current = setInterval(() => {
         setCount(prevCount => prevCount + 1);
       }, 1000);
     };

     const stopTimer = () => {
       if (timerRef.current) {
         clearInterval(timerRef.current);
       }
     };

     return (
       <div>
         <h1>Time: {count}s</h1>
         <button onClick={startTimer}>Start Timer</button>
         <button onClick={stopTimer}>Stop Timer</button>
       </div>
     );
   };

   export default Timer;

Explanation:

• timerRef.current is used to store the timer ID.
• startTimer and stopTimer functions use timerRef.current to manage the timer.
• Updating timerRef.current does not cause a re-render of the component.

Summary

• useRef creates a mutable ref object with a .current property.
• Use useRef to access DOM elements directly.
• Use useRef to keep mutable values that do not cause re-renders.

That’s it! useRef is a powerful and versatile hook that’s useful in many scenarios.