The useRef
Hook allows you to persist values between renders.
It can be used to store a mutable value that does not cause a re-render when updated.
It can be used to access a DOM element directly.
Does Not Cause Re-renders
If we tried to count how many times our application renders using the useState
Hook, we would be caught in an infinite loop since this Hook itself causes a re-render.
To avoid this, we can use the useRef
Hook.
Example:
Use useRef
to track application renders.
import { useState, useEffect, useRef } from "react";import ReactDOM from "react-dom/client";function App() { const [inputValue, setInputValue] = useState(""); const count = useRef(0); useEffect(() => { count.current = count.current + 1; }); return ( <> <input type="text" value={inputValue} onChange={(e) => setInputValue(e.target.value)} /> <h1>Render Count: {count.current}</h1> </> );}const root = ReactDOM.createRoot(document.getElementById('root'));root.render(<App />);
useRef()
only returns one item. It returns an Object called current
.
When we initialize useRef
we set the initial value: useRef(0)
.
It's like doing this: const count = {current: 0}
. We can access the count by using count.current
.
Run this on your computer and try typing in the input to see the application render count increase.
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Accessing DOM Elements
In general, we want to let React handle all DOM manipulation.
But there are some instances where useRef
can be used without causing issues.
In React, we can add a ref
attribute to an element to access it directly in the DOM.
Example:
Use useRef
to focus the input:
import { useRef } from "react";import ReactDOM from "react-dom/client";function App() { const inputElement = useRef(); const focusInput = () => { inputElement.current.focus(); }; return ( <> <input type="text" ref={inputElement} /> <button onClick={focusInput}>Focus Input</button> </> );}const root = ReactDOM.createRoot(document.getElementById('root'));root.render(<App />);
Tracking State Changes
The useRef
Hook can also be used to keep track of previous state values.
This is because we are able to persist useRef
values between renders.
Example:
Use useRef
to keep track of previous state values:
import { useState, useEffect, useRef } from "react";import ReactDOM from "react-dom/client";function App() { const [inputValue, setInputValue] = useState(""); const previousInputValue = useRef(""); useEffect(() => { previousInputValue.current = inputValue; }, [inputValue]); return ( <> <input type="text" value={inputValue} onChange={(e) => setInputValue(e.target.value)} /> <h2>Current Value: {inputValue}</h2> <h2>Previous Value: {previousInputValue.current}</h2> </> );}const root = ReactDOM.createRoot(document.getElementById('root'));root.render(<App />);
This time we use a combination of useState
, useEffect
, and useRef
to keep track of the previous state.
In the useEffect
, we are updating the useRef
current value each time the inputValue
is updated by entering text into the input field.
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