The Complete Guide to useRef() and Refs in React

React.useRef() is a hook that creates mutable values persisted between component renderings and references DOM elements.

In this post, you’ll learn how useRef() and refs (aka references) work in React. Interesting demos included.

1. Mutable values

useRef(initialValue) accepts one argument: the initial value of the reference. The hook returns a special value — named ref, or reference — which is an object having one property current:

const reference = useRef(initialValue);

reference; // => { current: <referenceValue> }

reference.current accesses the reference value, and reference.current = newValue updates the reference value. Pretty simple.

import { useRef } from 'react';

function MyComponent() {
  const reference = useRef(initialValue);
  const someHandler = () => {
    // Access reference value:
    const value = reference.current;
    // Update reference value:
    reference.current = newValue;  };

  // ...
}

There are 2 main rules to remember about the behavior of useRef() references:

1. The value of the reference is persisted (stays the same) between component re-renderings;
2. Updating a reference doesn’t trigger a component re-rendering.

Now, let’s see how useRef() works in practice.

1.1 Use case: logging button clicks

The component LogButtonClicks uses a reference to store the number of clicks on a button:

import { useRef } from 'react';

function LogButtonClicks() {
  const countRef = useRef(0);  
  const handle = () => {
    countRef.current++;    console.log(`Clicked ${countRef.current} times`);
  };

  console.log('I rendered!');

  return <button onClick={handle}>Click me</button>;
}

Try the demo.

const countRef = useRef(0) creates a references countRef initialized with 0.

When the button is clicked, handle function is invoked where the reference value is incremented: countRef.current++. The reference value is logged to the console.

What’s interesting is that updating the reference value countRef.current++ doesn’t trigger component re-rendering — 'I rendered!' is logged to console just once during initial rendering.

Now a reasonable question: what’s the main difference between references and state?

Reference and state diff

Let’s reuse the component LogButtonClicks from the previous section, but use useState() hook to count the number of button clicks:

import { useState } from 'react';

function LogButtonClicks() {
  const [count, setCount] = useState(0);  
  const handle = () => {
    const updatedCount = count + 1;
    console.log(`Clicked ${updatedCount} times`);
    setCount(updatedCount);  };

  console.log('I rendered!');

  return <button onClick={handle}>Click me</button>;
}

Try the demo.

Open the demo and click the button. Each time you click, you will see in the console the message 'I rendered!' — meaning that each time the state is updated, the component re-renders.

So, the 2 main differences between state and references:

1. Updating state does trigger component re-rendering while updating a reference doesn’t.
2. The state update is asynchronous (the state variable is updated after re-rendering), while the reference updates synchronously (the updated value is available right away)

From a higher point of view, references are used to store infrastructure data of the component, while the state stores information that is directly rendered on the screen.

1.2 Use case: implementing a stopwatch

The things you can store inside a reference are infrastructure information that involves some side-effect. For example, you can store into a reference the timer ids, different kinds of pointers (e.g. socket ids).

For example, the following component Stopwatch uses setInterval(callback, time) timer function to increase each second the counter of a stopwatch. The timer id is stored into a reference timerIdRef:

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

function Stopwatch() {
  const timerIdRef = useRef(0);  const [count, setCount] = useState(0);

  const startHandler = () => {
    if (timerIdRef.current) { return; }
    timerIdRef.current = setInterval(() => setCount(c => c + 1), 1000);  };

  const stopHandler = () => {
    clearInterval(timerIdRef.current);
    timerIdRef.current = 0;
  };

  useEffect(() => {
    return () => clearInterval(timerIdRef.current);
  }, []);

  return (
    <div>
      <div>Timer: {count}s</div>
      <div>
        <button onClick={startHandler}>Start</button>
        <button onClick={stopHandler}>Stop</button>
      </div>
    </div>
  );
}

Try the demo.

startHandler() function, which is invoked when the Start button is clicked, starts the timer and saves the timer id in the reference timerIdRef.current = setInterval(...).

To stop the stopwatch user clicks Stop button. The Stop button handler stopHandler() accesses the timer id from the reference and stops the timer clearInterval(timerIdRef.current).

Additionally, if the component unmounts while the stopwatch being active, the cleanup function of useEffect() is going to stop the timer too.

As you can see, in the stopwatch example the reference was used to store the infrastructure data — the active timer id.

Side challenge: can you improve the stopwatch by adding a Reset button? Share your solution in a comment below!

2. Access DOM elements

Another useful application of the useRef() hook is to access DOM elements. You can do it in 3 steps:

A) Define the reference to access the element const elementRef = useRef();

B) Assign the reference to ref attribute of the element: <div ref={elementRef}></div>;

C) After mounting, elementRef.current contains the DOM element.

import { useRef, useEffect } from 'react';

function AccessingElement() {
  const elementRef = useRef();
   useEffect(() => {
    const divElement = elementRef.current;  }, []);

  return (
    <div ref={elementRef}>      I'm an element
    </div>
  );
}

2.1 Use case: focusing an input

You would need to access DOM elements, for example, to focus on the input field when the component mounts.

To make it work you’ll need to create a reference to the input, and after mounting call the special method element.focus() on the element.

Here’s a possible implementation of the InputFocus component:

import { useRef, useEffect } from 'react';

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

  useEffect(() => {
    inputRef.current.focus();
  }, []);

  return <input ref={inputRef} type="text" />;
}

Try the demo.

const inputRef = useRef() creates a reference to hold the input element.

inputRef is then assigned to ref attribute of the input field: <input ref={inputRef} type="text" />.

React then, after mounting, sets inputRef.current to be the input element. Now you can set the focus to the input programatically: inputRef.current.focus().

Ref is null on initial rendering

During initial rendering, the reference supposed to hold the DOM element is empty:

import { useRef, useEffect } from 'react';

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

  useEffect(() => {
    // Logs `HTMLInputElement` 
    console.log(inputRef.current);
    inputRef.current.focus();
  }, []);

  // Logs `undefined` during initial rendering
  console.log(inputRef.current);
  return <input ref={inputRef} type="text" />;
}

Try the demo.

During initial rendering React still determines what is the output of the component, so there’s no DOM structure created yet. That’s why inputRef.current evaluates to undefined during initial rendering.

But useEffect(callback, []) hook invokes the callback right after mounting, thus the input element has already been created, and inputRef.current points to the actual input element.

3. Updating references restriction

The function scope of the functional component should either calculate the output, either invoke hooks.

That’s why updating a reference (as well as updating state) shouldn’t be performed inside the immediate scope of the component’s function.

The reference must be updated either inside a useEffect() callback or inside handlers (event handlers, timer handlers, etc).

import { useRef, useEffect } from 'react';

function MyComponent({ prop }) {
  const myRef = useRef(0);

  useEffect(() => {
    myRef.current++; // Good!
    setTimeout(() => {
      myRef.current++; // Good!    }, 1000);
  }, []);

  const handler = () => {
    myRef.current++; // Good!  };

  myRef.current++; // Bad!
  if (prop) {
    myRef.current++; // Bad!  }

  return <button onClick={handler}>My button</button>;
}

4. Summary

useRef() hook stores mutable values that persist between renderings, as well accesses DOM elements.

Calling const reference = useRef(initialValue) with the initial value returns a special object named reference. The reference object has a property current: you can use this property to access the reference value reference.current, or update the reference reference.current = newValue.

Between the component re-renderings, the value of the reference is persistent.

Updating a reference, contrary to updating state, doesn’t trigger component re-rendering.

References can also access DOM elements. Assign the reference to ref attribute of the element you’d like to access: <div ref={reference}>Element</div>. Then the element is available at reference.current.

Want to improve you React knowledge further? Follow A Simple Explanation of React.useEffect().

Challenge: write a custom hook useEffectSkipFirstRender() that works as useEffect(), only that it doesn’t invoke the callback after initial rendering (Hint: you need to use useRef()). Share your solution in a comment below!